My Ubuntu sessions were freezing up when I logged in and it took a while to figure out what was up, but the only consistent item was that certain files would attempt to start. However, if I started in safe mode all would work fine, or if iI started in Kubuntu that would work as well. So I searched for info on the Fail-safe mode and found the above linked article.
The useful piece for me was:
With this information I found the session file and edited it removing the ids of the files that I believed were causing the problem, logged off safe-mode and then back on in regular Gnome and it was fixed. :o)gnome-session uses the contents of the ~/.gnome/session file for starting up as specified by the "Current Sesssion" key in the ~/.gnome/session-options file. Various default values are provided in case the file entry does not exist.
If the session file does not exist, gnome-session will use the contents of the
/usr/share/gnome/default.session file.