It has been almost a month since you had this error, so you've probably
already fixed it. But, in case you haven't and for those people who
are also having this problem, check the suexec_log for apache. It will
most likely tell you why your script is failing. I would guess without
even looking at the log that you have write permissions for others on
your script (bugzilla) directory. suexec doesn't like this.