Hi JAM,
Can you check your NWBC setup as per below links
SAP NetWeaver Business Client 4.0 Overview
http://scn.sap.com/docs/DOC-33288
Additionally check whether FQDN is being used to launch NWBC
http://<fully qualified host name>:<http port>/sap/bc/nwbc/nwbc_launch
Hope this helps.
Regards,
Deepak Kori