Hi Jon,
Whenever something unexpected happens, I think it's best to find out if a request has been sent out correctly from the client proxy and received by the web service.
If the web service is an SAP web service, you can use the following
1. SRT_UTIL transaction. You can find out more from the link below
http://wiki.scn.sap.com/wiki/display/ABAPConn/ABAP+Web+Service+Monitors
2. You may want to enable logging and tracing as well.
http://help.sap.com/saphelp_nwpi711/helpdata/en/2f/9eddbb74b84775931ca9f2297c77be/content.htm
Hope this helps.
Regards,
Stevanic