After logging into my Ubuntu 9.04 machine I'm greeted with the following message "Cannot find or run the base session script. Running Gnome in failsafe session instead". The reason for this was I had messed up my permissions and the following fixed it:
After logging in and recieving the errors message press Ctrl-Alt-F1 to drop back into command line. Then run the following:
Sudo chmod 755 /etc/gdm/Xsession
Ubuntu Linux Permissions Gnome