I'm getting this error related to the creation of cache objects when a page is requested by a user, does this ring any bells? I'm not sure where to look for a solution (there are no other discussions with a solution, only a few other users with the same issue...)

Here are some error details:

Server Error in '/' Application. 
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This document already has a 'DocumentElement' node. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidOperationException: This document already has a 'DocumentElement' node.

Source Error: 
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. 

Stack Trace: 

[InvalidOperationException: This document already has a 'DocumentElement' node.]
   System.Xml.XmlDocument.IsValidChildType(XmlNodeType type) +3957861
   System.Xml.XmlDocument.AppendChildForLoad(XmlNode newChild, XmlDocument doc) +28
   System.Xml.XmlLoader.LoadDocSequence(XmlDocument parentDoc) +37
   System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace) +129
   System.Xml.XmlDocument.Load(XmlReader reader) +108
   System.Xml.XmlDocument.Load(String filename) +87
   umbraco.cms.businesslogic.web.Access.get_AccessXml() +154
   umbraco.cms.businesslogic.web.Access.getPage(Int32 documentId) +15
   umbraco.cms.businesslogic.web.Access.IsProtected(Int32 DocumentId, String Path) +146
   umbraco.requestHandler..ctor(XmlDocument _umbracoContent, String url) +3445
   umbraco.UmbracoDefault.Page_PreInit(Object sender, EventArgs e) +818
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.EventHandler.Invoke(Object sender, EventArgs e) +0
   System.Web.UI.Page.OnPreInit(EventArgs e) +8694814
   System.Web.UI.Page.PerformPreInit() +31
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +282

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Version Information: Microsoft .NET Framework Version:2.0.50727.3053; ASP.NET Version:2.0.50727.3053 
Request Details
Session Id: g5d05n45djfy4o45jrlypg45    Request Type:   GET                     
Time of Request:  16/08/2010 12:12:14 Status Code:    500                     
Request Encoding: Unicode (UTF-8) Response Encoding:  Unicode (UTF-8)                     
Trace Information
Category   Message From First(s)   From Last(s)                        
aspx.page Begin PreInit                               
umbracoInit   handling request    0,0209018941337438  0,020902                        
request handler   current url '/nl/het-project'   0,193826627615301   0,172925                        
umbracoRequestHandler xpath: '/root/node/node [@urlName = "nl"]/node [@urlName = "het-project"] | /root/node [@urlName = "het-project"]'  0,263074831822587   0,069248                        
umbracoRequestHandler Just before xPath query (False, '/root/node/node [@urlName = "nl"]/node [@urlName = "het-project"] | /root/node [@urlName = "het-project"]')    0,263177240465196   0,000102                        
umbracoRequestHandler pageXPathQueryStart: '/root'    0,263248775725443   0,000072                        
umbracoRequestHandler Adding to cache... ('/nl/het-project')  0,264494494327575   0,001246                        
umbracoRequestHandler After xPath query   0,264564417650077   0,000070                        
umbracoRequestHandler Access checking started 0,264712084544781   0,000148                        
Unhandled Execution Error 
This document already has a 'DocumentElement' node.
  at System.Xml.XmlDocument.IsValidChildType(XmlNodeType type)
  at System.Xml.XmlDocument.AppendChildForLoad(XmlNode newChild, XmlDocument doc)
  at System.Xml.XmlLoader.LoadDocSequence(XmlDocument parentDoc)
  at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace)
  at System.Xml.XmlDocument.Load(XmlReader reader)
  at System.Xml.XmlDocument.Load(String filename)
  at umbraco.cms.businesslogic.web.Access.get_AccessXml()
  at umbraco.cms.businesslogic.web.Access.getPage(Int32 documentId)
  at umbraco.cms.businesslogic.web.Access.IsProtected(Int32 DocumentId, String Path)
  at umbraco.requestHandler..ctor(XmlDocument _umbracoContent, String url)
  at umbraco.UmbracoDefault.Page_PreInit(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.EventHandler.Invoke(Object sender, EventArgs e)
  at System.Web.UI.Page.OnPreInit(EventArgs e)
  at System.Web.UI.Page.PerformPreInit()
  at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) 0,333269368907132   0,068557                        
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