Jan Vroonhof writes:
AUC TeX works fine on both stock Emacs and (S)XEmacs has been doing so for a very very long time. This is mostly due to the work of Per Abrahamsen (clap clap) in particular his easymenu package. Which leads to what is probably the problem...
Most problems with AUC TeX are one of two things:
Fix: make sure you configure AUC TeX properly before installing.
locate-library and remove old versions to make sure it
only finds the one that came with SXEmacs.