internal server error with fedex web services mod

I tried installing the newest fedex web services mod by Numinix that I could find, (1.3.1). I put all the folders in the proper places within the "includes" folder. It causes the shipping page on my website to crash. "500 internal server error." I tried to install an older version of this mod a while back (1.1.2). I deleted all the old files, installed the new ones, same problem. Also, I hit "remove" in zencart admin for the old Fed-Ex api's that no longer work as of May 31st, but that didn't help any. Also, I tried putting all the files for the mod into the "admin/includes" folder instead, but that didn't help either. I then removed the files from the "admin/includes" folder. I'm not seeing any other fedex web services mods available to try either.

usually server errors are problems with either corrupted files, or permissions. I know one of my biggest problems is uploading files under a different username than that of the website. You might check and make sure your permissions are set correctly with the files you uploaded.

http://www.zen-cart.com/content.php?105-why-am-i-getting-500-internal-server-error