I would recommend tracing the call from pega and in the tracer turning on soap messages. This will show you the message Pega is sending and you can then compare that to the SOAP UI message to see what is different.
The service is returning some response which Pega is failing to parse (failure is after handleresponse). Looks like you are masking the response due to sharing of data on public forum. I would suggest you to create a SR so that Pega GCS can have a screen share to debug further.