WHat do you get if you run
dpkg -l gnome-session? Here's what I get un ubuntu 8.04.3
Code:
c@CW8:~$ dpkg -l gnome-session
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-f/Unpacked/Failed-cfg/Half-inst/t-aWait/T-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name Version Description
+++-=================================-=================================-==================================================================================
ii gnome-session 2.22.1.1-0ubuntu2 The GNOME 2 Session Manager
If it doesn't show "i" in the first column then it's not installed and you need to install it. Maybe gnome-light doesn't install it.