I have a user that gets a blank screen after they login using a tightVNC session.

1) They are attempting to login to Redhat 4.8 ES.
2) They will first be presented the gnome login screen.
3) After giving their credentials, the screen just becomes blank - nothing else.
4) Other users can run tightVNC to this server without a problem.
5) This is localized to this user only. This user also can't login using tightVNC from other Windows workstations.
6) The user can login using 'ssh' from another server.
7) This user has been able to run tightVNC successfully in the past.

It appears to me that there may be something wrong with this user's profile - any ideas?

They may have changed some gnome related preference, you could try deleting the following in their home directory :

.gnome .gnome2 .gconf .gconfd .metacity

Please check display settings of your vnc viewer.
Another option is to backup following folders.

.gnome .gnome2 .gconf .gconfd .metacity

Then delete these folders.
logout and login you will get default settings.
Things should work well after that if it is problem with config files.

thank you