Hi Michel

This is a long shot but have you tried to change the value of MaxPostSize
Registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSOAP\SOAPISAP

MaxPostSize — the maximum size of the SOAP message that you can POST to the ISAPI handler.

The SOAP Help says that you may need to increase the default size (100 KB) if your service accepts large SOAP messages. Maby it also applies to the size of the reply.

-Charles