I boot up my RedHat 6.0 and after login I often, say 1 in 7
times, will get a desktop background login missing all the
icons and taskbar, showing only a mouse 'X' and a RedHat
logo on the screen. I then have to restart the session.
More information is required to debug.
You might try the new GNOME RPMs from 6.1, they potentially solve this problem.