Error number 51 - Unable to find a schema in database.

Hi Brian,
 
I get a strange Error message: "Analysis_PU_02_Duplicate_Name_Address_VATNumber",51,"Unable to find a schema in database."
 
I executed my script several times and 2 out of 5 times I get said error.
I always execute the script from the same folder and have the same working folder.
 
Here is my Code:
 
Function Analysis_PU_02_Duplicate_Name_Address_VATNumber
        On Error GoTo ErrHandler 
        Dim dbname As String
        Dim finname As String
 
        finname = "PU_02_Duplicate_Name_Address_VATNumber"
 
        dbname = workingdirectory + "\03 Results\VendorMaster_without_Employees.IDM"
        If fileexists(dbname)=false Then
              Call Analysis_VendorMaster_without_Employees
        End If
 
        Set db = Client.OpenDatabase(dbname)
        Set task = db.DupKeyDetection
        task.DisableProgressNotification = True
        task.IncludeAllFields
        task.AddKey "NAME_1", "A"
        task.AddKey "CITY", "A"
        task.AddKey "POSTAL_CODE", "A"
        task.AddKey "HOUSE_NUMBER_AND_STREET", "A"
        task.AddKey "VAT_REGISTRATION_NUMBER", "A"
        task.OutputDuplicates = TRUE
        dbName = workingdirectory + "\03 Results\" + finname + ".IDM"
        task.PerformTask dbName, ""
 
        Client.CloseAll
 
        Dim copycomplete As Boolean
        copycomplete = moveIt(finname, "Duplicate Name Address VATNumber")
 
        Set task = Nothing
        Set db = Nothing
 
        Exit Function
ErrHandler:
        If Err.Number = 0 Then
              Write #1, Now, " - ERROR - " , "Analysis_PU_02_Duplicate_Name_Address_VATNumber", Err.Number, Err.Description, "Error Not defined"
        Else
              Write #1, Now, " - ERROR - " , "Analysis_PU_02_Duplicate_Name_Address_VATNumber", Err.Number, Err.Description
        End If
        errorOccurred = TRUE
        'resume next
 
End Function
 
Have you ever had this error message? Any thoughts on how to fix it?
 
Thanks in advance,
Steve