WSDL soapRPC/HTTP with BAPI

I’m trying to create a Web Service that will execute a BAPI in SAP using the soapRPC over HTTP settings (default settings). I receive the following SOAP Fault String when I execute the Web Service Connector:

[B2BSERV.0088.9133] Error while encoding RPC output

Is anyone familiar with this error or has anyone had any success in this area.

Thanks in advance,
DJ Harris