EnableBackgroundProcessing while opening large assembly drawing makes SWX freeze, only in SWX 2011?

Since we updated from swx 2010 to 2011 SP04, using the 'EnableBackgroundProcessing' method in VBA while open drawings of large assemblies results in swx freezing, and needing to be forcibly closed with the task manager.

Removing the EnableBackgroundProcessing code, stops swx freezing but, it takes considerably longer to open drawings.

Drawings of smaller parts / assemblies are not affected and open fine.

Here is the code copied directly from SWX API help:

'---------------------------------------------------------------------------

' Preconditions: Specified drawing document exists.

'

' Postconditions: Specified drawing document opens.

'---------------------------------------------------------------------------

Option Explicit

Dim swApp As SldWorks.SldWorks

Dim swDrawing As SldWorks.DrawingDoc

Dim strFileName As String

Dim longstatus As Long

Dim longwarnings As Long

Sub main()

Set swApp = Application.SldWorks

strFileName = "c:\Program Files\SolidWorks Corp\SolidWorks\samples\tutorial\advdrawings\foodprocessor.slddrw"

swApp.EnableBackgroundProcessing = True

Set swDrawing = swApp.OpenDoc6(strFileName, 3, 0, _

        "", longstatus, longwarnings)

While (swApp.IsBackgroundProcessingCompleted(strFileName) = False)

    Debug.Print ("Background processing ongoing...")

Wend

swApp.EnableBackgroundProcessing = False

Set swApp = Nothing

End Sub

Any ideas?

SolidworksApi macros