diagnose session?

[Paul Emsley chem gla ac uk]

       Hi,

       How do I diagnose my (gdm) session?

       If I try to log in with gdm Gnome session, then I get logged
      back out again (back to gdm screen).
      
      If I set to Failsafe and use gnome-session in the xterm, then
      all is as it should be.

      (This started happening after I installed helix gnome,
      incidently).


      Thanks for your help,

      Paul.