It might be a know issue with PB, see:
http://search.sybase.com/kbx/changerequests?bug_id=644113
Or, as the message indicates, it may mean that the service is returning something that doesn't match what the WSDL said it would return.
wcf - WebService error when accessed from PowerBuilder 12 aplication - Stack Overflow
It's really hard to tell with the limited information here. It would help to know what the definition of TransactionType is.
It would be very helpful if the service was publically accessible. That way somebody else could hit it and see if there was anything obviously wrong.