I am takeing a closer look at the error and notice it was not possible to execute the sql-connection. I fixed some issues with open connections, but didn't role this to production yet. Looks like this issue is connected to this fix. I will investigate further.

We are also getting this problem!

This problem still occures on our site. The following errors occure before this happens:

System.InvalidOperationExceptionThere is already an open DataReader associated with this Command which must be closed first.

System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> Umbraco.Courier.Core.Exceptions.RetrieveException: Error retrieving item [3e2917b5-3801-451b-b845-1d9af97689a3] from provider [d8e6ad83-e73a-11df-9492-0800200c9a66]. ---> NHibernate.Exceptions.GenericADOException: could not execute query
[ SELECT this_.id as id32_1_, this_.createDate as createDate32_1_, this_.level as level32_1_, this_.nodeObjectType as nodeObje4_32_1_, this_.path as path32_1_, this_.sortOrder as sortOrder32_1_, this_.text as text32_1_, this_.trashed as trashed32_1_, this_.uniqueID as uniqueID32_1_, this_.nodeUser as nodeUser32_1_, this_.parentID as parentID32_1_, umbracouse2_.id as id38_0_, umbracouse2_.defaultToLiveEditing as defaultT2_38_0_, umbracouse2_.startMediaID as startMed3_38_0_, umbracouse2_.startStructureID as startStr4_38_0_, umbracouse2_.userDefaultPermissions as userDefa5_38_0_, umbracouse2_.userDisabled as userDisa6_38_0_, umbracouse2_.userEmail as userEmail38_0_, umbracouse2_.userLanguage as userLang8_38_0_, umbracouse2_.userLogin as userLogin38_0_, umbracouse2_.userName as userName38_0_, umbracouse2_.userNoConsole as userNoC11_38_0_, umbracouse2_.userPassword as userPas12_38_0_ FROM umbracoNode this_ left outer join umbracoUser umbracouse2_ on this_.nodeUser=umbracouse2_.id WHERE this_.uniqueID = @p0 ]
Positional parameters:  #0>3e2917b5-3801-451b-b845-1d9af97689a3
[SQL: SELECT this_.id as id32_1_, this_.createDate as createDate32_1_, this_.level as level32_1_, this_.nodeObjectType as nodeObje4_32_1_, this_.path as path32_1_, this_.sortOrder as sortOrder32_1_, this_.text as text32_1_, this_.trashed as trashed32_1_, this_.uniqueID as uniqueID32_1_, this_.nodeUser as nodeUser32_1_, this_.parentID as parentID32_1_, umbracouse2_.id as id38_0_, umbracouse2_.defaultToLiveEditing as defaultT2_38_0_, umbracouse2_.startMediaID as startMed3_38_0_, umbracouse2_.startStructureID as startStr4_38_0_, umbracouse2_.userDefaultPermissions as userDefa5_38_0_, umbracouse2_.userDisabled as userDisa6_38_0_, umbracouse2_.userEmail as userEmail38_0_, umbracouse2_.userLanguage as userLang8_38_0_, umbracouse2_.userLogin as userLogin38_0_, umbracouse2_.userName as userName38_0_, umbracouse2_.userNoConsole as userNoC11_38_0_, umbracouse2_.userPassword as userPas12_38_0_ FROM umbracoNode this_ left outer join umbracoUser umbracouse2_ on this_.nodeUser=umbracouse2_.id WHERE this_.uniqueID = @p0] ---> System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.
   at System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command)
   at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader()
   at NHibernate.AdoNet.AbstractBatcher.ExecuteReader(IDbCommand cmd)
   at NHibernate.Loader.Loader.GetResultSet(IDbCommand st, Boolean autoDiscoverTypes, Boolean callable, RowSelection selection, ISessionImplementor session)
   at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
   at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
   --- End of inner exception stack trace ---
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Loader.Criteria.CriteriaLoader.List(ISessionImplementor session)
   at NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results)
   at NHibernate.Impl.CriteriaImpl.List(IList results)
   at NHibernate.Impl.CriteriaImpl.List[T]()
   at Umbraco.Courier.Persistence.V4.NHibernate.Helpers.DocumentHelper.Get(Guid uniqueId, ISession session) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Persistence.NHibernate\Helpers\DocumentHelper.cs:line 23
   at Umbraco.Courier.Persistence.V4.NHibernate.Persisters.DocumentItem.RetrieveItem[T](ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Persistence.NHibernate\Persisters\Document.cs:line 80
   at Umbraco.Courier.Core.ItemCrudProvider.RetrieveItem[T](ItemIdentifier itemId)
   --- End of inner exception stack trace ---
   at Umbraco.Courier.Core.ItemCrudProvider.RetrieveItem[T](ItemIdentifier itemId)
   at Umbraco.Courier.ItemProviders.DocumentItemProvider.HandlePack(ItemIdentifier id) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Providers\ItemProviders\ContentItemProvider.cs:line 79
   at Umbraco.Courier.Core.ItemProvider.Package(ItemIdentifier id)
   at Umbraco.Courier.RepositoryProviders.Local.Package(ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.RepositoryProviders\Local\Local.cs:line 227
   at Umbraco.Courier.Cachehandler.V4.CacheHandler._sendToCache(ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.CacheHandler.V4\Cachehandlers\CacheHandler.cs:line 211
   at Umbraco.Courier.Cachehandler.V4.CacheHandler.Document_AfterPublish(Document sender, PublishEventArgs e) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.CacheHandler.V4\Cachehandlers\CacheHandler.cs:line 156
   at umbraco.cms.businesslogic.web.Document.PublishEventHandler.Invoke(Document sender, PublishEventArgs e)
   at umbraco.cms.businesslogic.web.Document.PublishWithResult(User u)
   at umbraco.cms.presentation.editContent.Publish(Object sender, EventArgs e)
   at System.EventHandler.Invoke(Object sender, EventArgs e)
   at System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e)
   at System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
        

after this error occures I get the following error:

System.InvalidOperationExceptionInvalid attempt to call Read when reader is closed.

System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> Umbraco.Courier.Core.Exceptions.RetrieveException: Error retrieving item [473293c7-ee64-468f-b193-3af5e5ea9980] from provider [e0472594-e73b-11df-9492-0800200c9a66]. ---> NHibernate.Exceptions.GenericADOException: could not execute query
[ select TOP (@p0) cmscontent0_.id as id4_, cmscontent0_.VersionDate as VersionD2_4_, cmscontent0_.VersionId as VersionId4_, cmscontent0_.contentId as contentId4_ from cmsContentVersion cmscontent0_, cmsContent cmscontent1_ where cmscontent0_.contentId=cmscontent1_.nodeId and cmscontent1_.nodeId=@p1 order by cmscontent0_.id desc ]
  Name:p1 - Value:5571
[SQL: select TOP (@p0) cmscontent0_.id as id4_, cmscontent0_.VersionDate as VersionD2_4_, cmscontent0_.VersionId as VersionId4_, cmscontent0_.contentId as contentId4_ from cmsContentVersion cmscontent0_, cmsContent cmscontent1_ where cmscontent0_.contentId=cmscontent1_.nodeId and cmscontent1_.nodeId=@p1 order by cmscontent0_.id desc] ---> System.InvalidOperationException: Invalid attempt to call Read when reader is closed.
   at System.Data.SqlClient.SqlDataReader.ReadInternal(Boolean setTimeout)
   at NHibernate.Driver.NHybridDataReader.Read()
   at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
   at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies)
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
   --- End of inner exception stack trace ---
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.List(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Hql.Ast.ANTLR.QueryTranslatorImpl.List(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Engine.Query.HQLQueryPlan.PerformList(QueryParameters queryParameters, ISessionImplementor session, IList results)
   at NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters queryParameters, IList results)
   at NHibernate.Impl.AbstractSessionImpl.List(IQueryExpression queryExpression, QueryParameters parameters)
   at NHibernate.Impl.ExpressionQueryImpl.List()
   at NHibernate.Linq.NhQueryProvider.ExecuteQuery(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery)
   at NHibernate.Linq.NhQueryProvider.Execute[TResult](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at Umbraco.Courier.Persistence.V4.NHibernate.Helpers.DocumentHelper.GetLatestVersion(Int32 id, ISession session) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Persistence.NHibernate\Helpers\DocumentHelper.cs:line 236
   at Umbraco.Courier.Persistence.V4.NHibernate.Persisters.ContentPropertyDataItem.RetrieveItem[T](ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Persistence.NHibernate\Persisters\ContentPropertyData.cs:line 99
   at Umbraco.Courier.Core.ItemCrudProvider.RetrieveItem[T](ItemIdentifier itemId)
   --- End of inner exception stack trace ---
   at Umbraco.Courier.Core.ItemCrudProvider.RetrieveItem[T](ItemIdentifier itemId)
   at Umbraco.Courier.ItemProviders.PropertyItemProvider.HandlePack(ItemIdentifier id) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Core\Umbraco.Courier.Providers\ItemProviders\PropertyItemProvider.cs:line 87
   at Umbraco.Courier.Core.ItemProvider.Package(ItemIdentifier id)
   at Umbraco.Courier.RepositoryProviders.Local.Package(ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.RepositoryProviders\Local\Local.cs:line 227
   at Umbraco.Courier.Cachehandler.V4.CacheHandler._sendToCache(ItemIdentifier itemId) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.CacheHandler.V4\Cachehandlers\CacheHandler.cs:line 211
   at Umbraco.Courier.Cachehandler.V4.CacheHandler.Document_AfterSave(Document sender, SaveEventArgs e) in c:\Program Files (x86)\teamcity\buildAgent\work\872c402d3442319c\Contrib\Providers\Umbraco.Courier.CacheHandler.V4\Cachehandlers\CacheHandler.cs:line 166
   at umbraco.cms.businesslogic.web.Document.SaveEventHandler.Invoke(Document sender, SaveEventArgs e)
   at umbraco.cms.businesslogic.web.Document.Save()
   at umbraco.cms.presentation.editContent.Save(Object sender, EventArgs e)
   at System.EventHandler.Invoke(Object sender, EventArgs e)
   at umbraco.controls.ContentControl.saveClick(Object Sender, ImageClickEventArgs e)
   at umbraco.controls.ContentControl.savePublish(Object Sender, ImageClickEventArgs e)
   at System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e)
   at System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
        

Then finally we recieve the message reported. For this moment it means we have to deinstall courier to get a stable enviorment.

is working on a reply...