MailMerge fails with PowerBuilder after Office SP3

We have a PowerBuilder application that uses Word and its mail merge
capabilities to produce letters. We have recently applied SP3 to Office.
This installed version 10.0.6612 of winword.exe. Now, when trying to access
a document for merging we are getting an error stating that it is not able to
access external object property 'xxxxxx'.

The instantiation of the OLE object succeeds.
The opening of the Document succeeds.
The accessing the ActiveDocument fails.

Under version 10.0.4219 this worked without a problem. I was able to
confirm this version change was the problem by swapping winword 10.0.6612 and
10.0.4219 back and forth.

Any ideas?

Thanks in advance