You are welcome, and I understand that sometimes getting perl based scripts to run correctly is challenging (particularly MT - it has always been that way).
Beside the permissions issue(s), the second most common cause of 500 Internal Server Errors with perl scripts has to do with non-*nix style line endings.
Files edited on Winbloze or older MAC systems using many (most) common editors have incorrect line-ending character sequences, and this often causes errors, as does uploading the script files in Binary mode instead of “ASCII” mode (depending upon your FTP client, a “related” issue).
I’ve often gotten scripts that were not running to work by simply starting over after deleting all the files from the server, making sure that all files were saved in an editor that uses *nix line endings, and re-uploading them to the directory in ASCII mode.
It would also help to see what is causing the problem if you inspect the contents of your apache error log for additional clues as to where the problem lies.