@Dragon
I had the same problem. I fixed it in ubb_forum_summary.cgi
Look for
if ($thisforuminfo[6] eq 'private') { $exact_path .= "/private-$thisforuminfo[7]"; }
this line is 2x in ubb_forum_summary.cgi
After each I added this line:
if ($thisforuminfo[6] eq 'hidden') { $exact_path .= "/private-$thisforuminfo[7]"; }
now it works