I see that there have been other similar posts, but the underlying problems seem to vary. I am not competent to troubleshoot myself, could you please walk me through it:
I have recently upgraded from 10.04 to 12.04 working under GNOME. The installation is fine (with occasional "internal errors") when I specify GNOME Classic at logon, but gnome-shell does not load (even though installed). It does load when I specify GNOME at login.
So it seems that GNOME fallback is running even though I specify GNOME Classic?
If possible I would like to have GNOME Classic with gnome-shell working to be able to use Gnome extensions.
Looking forward to your advice, thanks so much, John
P.S. I noticed that when I originally intalled GNOME I followed web advice to install only gnome-session-back, and later installed gnome-shell. To be sure that was not the problem, I completely disinstalled gnome-session-fallback and gnome-shell, then rebooted in Unity and installed gnome-shell (which also installs automatically gnome-session-fallback). Same result: when loggin in with GNOME Classic, gnome-shell does not load and I apparently get a GNOME fallback session. Sometimes (maybe 10%) I get session with no top and bottom task bars (representing failed GNOME Classic?); in that case I close and reopen the session specifying GNOME Classic and I get a perfectly useable interface without gnome-shell loaded.