System.ArgumentException: An entry with the same key already exists.

Hi, the integration with AX seems to be working just fine but all of a sudden we get this error in Service Log when trying to Generate the reports in Designer. I just don't get it. My first try was to remove the existing datamart and create a new one as that usually solves all problems with MR

System.ArgumentException: An entry with the same key already exists.

   at System.Collections.Generic.TreeSet`1.AddIfNotPresent(T item)

   at System.Collections.Generic.SortedDictionary`2.Add(TKey key, TValue value)

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.GLLinkAdapter.GetAllGLBooks()

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.GLLinkAdapter.CreateDefaultBalanceFilters()

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.ReportProcessor.SetReportPeriodsCovered()

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.ReportProcessor.SetupReportForRun()

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.ReportGenerator.ProcessReport(Definition definition, Action`1 resultHandler)

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.EngineController.GenerateReport(Action`1 resultHandler)

   at Microsoft.Dynamics.Performance.Reporting.Engine.Server.EngineController.Run(NativeReport repositoryReport, Definition definition)

   at Microsoft.Dynamics.Performance.Reporting.Scheduler.ReportRunner.RunReport(String reportDefinitionXml, Guid repositoryId, Guid generatedByPrincipalId)

Does anybody have a clue what this is about and how to solve it? The other logs looks fine. No errors. MR cu7 and AX 2012 CU7