Gnome xml parsing error & only allows one login

["Allen Williams" <anw@csunv.com>]

When I select Gnome as my desktop environment, I get an XML parsing error
dialog, with no close button but a window decoration that lets me close it.
When I close it, the system just hangs, and I have to CTL-ALT F1 to get a
console window and kill the X process.  The error is:

XML parsing error: xml processing instruction not at start of external
entity.
Location: chrome://mozapps/content/profile/ProfileSelection.xul
Line number 1, column 1:

(Isn't THAT  a user-friendly message?)

When I use a KDE session, there is an intermittent error.  Everything seems
OK until I logout, then sometimes I get a splash screen, like what's
supposed to be the background, but no login dialogue.

TIA