Hmm...sounds like the Riverbed is working fine. Have you examined the session trace for the connection attempt through NCM?
Just in case you haven't done that before:
1. Go to NCM Settings > Advanced, and Enable Session Tracing.
2. Test the login from NCM
3. Hop on your NCM server and open up the session trace for that session. The files will be located in "{NCMInstallDir}\Session-Trace"
