I just ran into a crash with Gnus, trying to enter a group.
Of course, this bug is probably a little bit hard to
reproduce, as I can't provide you with the nntp data :-)
Anyway, I don't get a lisp backtrace, the only thing I can
get is a gdb backtrace when I start XEmacs from within gdb.
I'm not sure, it is really helpful, but here it is:
Put a breakpoint on assert_failed and call debug_backtrace().