@ gizzy
I looked at the sticky topics zip, and saw it looks at &is_admin_or_mod() which is located in ubb_lib.cgi line 254-ish.
During the installation of megamod, did you modify this sub? The default line 261
if ($profile[8] eq 'Administrator') {
while yours should look like
if ($profile[8] =~ m/^Administrator|MegaModerator$/) {
or something like that. Does it look similar?