Problem with PowerPivot refresh code

Private Function doXMLA(cnn, databaseID As String, Optional dimensionID As String = "", Optional timeout As Long = 30)
Dim xmla As String
Dim lRet
Dim comm As Object ' ADODB.Command
    ' The XMLA Batch request
    If dimensionID = "" Then
     xmla = "<Batch xmlns=""http://schemas.microsoft.com/analysisservices/2003/engine""><Parallel><Process xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:ddl2=""http://schemas.microsoft.com/analysisservices/2003/engine/2"" xmlns:ddl2_2=""http://schemas.microsoft.com/analysisservices/2003/engine/2/2"" xmlns:ddl100_100=""http://schemas.microsoft.com/analysisservices/2008/engine/100/100""><Object><DatabaseID><<<DatabaseID>>></DatabaseID></Object><Type>ProcessFull</Type><WriteBackTableCreation>UseExisting</WriteBackTableCreation></Process></Parallel></Batch>"
     xmla = Replace(xmla, "<<<DatabaseID>>>", databaseID)
    Else
     xmla = "<Batch xmlns=""http://schemas.microsoft.com/analysisservices/2003/engine""><Parallel><Process xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:ddl2=""http://schemas.microsoft.com/analysisservices/2003/engine/2"" xmlns:ddl2_2=""http://schemas.microsoft.com/analysisservices/2003/engine/2/2"" xmlns:ddl100_100=""http://schemas.microsoft.com/analysisservices/2008/engine/100/100""><Object><DatabaseID><<<DatabaseID>>></DatabaseID><DimensionID><<<DimensionID>>></DimensionID></Object><Type>ProcessFull</Type><WriteBackTableCreation>UseExisting</WriteBackTableCreation></Process></Parallel></Batch>"
     xmla = Replace(xmla, "<<<DatabaseID>>>", databaseID)
     xmla = Replace(xmla, "<<<DimensionID>>>", dimensionID)
    End If
    Set comm = CreateObject("ADODB.command")
    comm.CommandTimeout = timeout
    comm.CommandText = xmla
    Set comm.ActiveConnection = cnn
    comm.Execute
    ' Make the request
    'On Error Resume Next - comment out on error as most are not trappable within VBA !!!
    'lRet = cnn.Execute(xmla)
    'If Err Then Stop
    doXMLA = "OK"
End Function

I have an Excel 2010 workbook with PowerPivot which is connected to an Access 2010 query. The workbook uses Goban Saor's VBA code to refresh the data. Recently I made a small change to the Access query. Now the refresh code stops at line "comm.Execute" (about 8 lines from the bottom) in the attached function with Run-Time error '2147467259 (80004005)' "The current operation was cancelled because another operation in the transaction failed"  All I did was make a small change to the acccess query - nothing else. I can manually refresh the PowerPivot window and the pivot table without any problem. Any ideas of what may be causing this?