Hi there I'm using:

 - Umbraco v4.0.0 (Assembly version: 1.0.3317.32692)
 - MySQL
 - ASP .NET 3.5
 - XP and IIS 5.1

I originally had Umbraco installed on a Sql Server 2005 database where I created 3 different member types with various properties. I loaded data against this and decided at some point to switch to MySQL. It all seems to work fine except for the fact that I can't edit my member types anymore as I'm served with the following error:

[InvalidCastException]: Specified cast is not valid.
   at umbraco.DataLayer.SqlHelper`1.ConvertScalar[T](Object scalar)
   at umbraco.DataLayer.SqlHelper`1.ExecuteScalar[T](String commandText, IParameter[] parameters)
[SqlHelperException]: Umbraco Exception (DataLayer): SQL helper exception in ExecuteScalar
   at umbraco.DataLayer.SqlHelper`1.ExecuteScalar[T](String commandText, IParameter[] parameters)
   at umbraco.cms.businesslogic.member.MemberType.MemberCanEdit(PropertyType pt)
   at umbraco.cms.presentation.members.EditMemberType.dgEditExtras_itemdatabound(Object sender, DataGridItemEventArgs e)
   at System.Web.UI.WebControls.DataGrid.OnItemDataBound(DataGridItemEventArgs e)
   at System.Web.UI.WebControls.DataGrid.CreateItem(Int32 itemIndex, Int32 dataSourceIndex, ListItemType itemType, Boolean dataBind, Object dataItem, DataGridColumn[] columns, TableRowCollection rows, PagedDataSource pagedDataSource)
   at System.Web.UI.WebControls.DataGrid.CreateControlHierarchy(Boolean useDataSource)
   at System.Web.UI.WebControls.BaseDataList.OnDataBinding(EventArgs e)
   at System.Web.UI.WebControls.BaseDataList.DataBind()
   at umbraco.cms.presentation.members.EditMemberType.setupExtraEditorControls()
   at umbraco.cms.presentation.members.EditMemberType.Page_Load(Object sender, EventArgs e)
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at umbraco.BasePages.BasePage.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
[HttpUnhandledException]: Exception of type 'System.Web.HttpUnhandledException' was thrown.
   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.ProcessRequestWithNoAssert(HttpContext context)
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at ASP.umbraco_members_editmembertype_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\80eb830a\34fd6ea9\App_Web_editmembertype.aspx.590a8cbd.huwnweem.0.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Any help would be greatly appreciated.

Alex