i edited the functions file exactly as stated (not the functions exec_mail_queue();, just exec_mail_queue()

to
// exec_mail_queue(); // Paul M - Cron Mail Queue Hack //
and I get the functions.php syntax error. The line exec_mail_queue is in there twice, once with functions before, once without. I tried changing both, and tried changing just the one with function before it, and tried just with the one that doesn't have function before it. All combos cause the syntax error. When I change the line back, the error goes away.
vbulletin 4.1.1
any ideas Paul? did something in the latest version "break" your modification?