Ok, I am obviously doing something wrong. I've dropped this into 4 different installations - 3 of which were 5.45c, and one brand new, unhacked 5.47c. All I've done is copied the text to a file called active.cgi, sent it to the cgi directory that UBB is in (ASCII mode), and CHMOD to 755. Even tried CHMOD to 777 and got nothing on any of the installations - all give 500 errors. Path to Perl is correct, and the forums do work fine.
I'm missing a step here (and probably a clue). My kingdom to anyone who can help.
