A 500 Internal Server Error appearing after a user attempts to register may be caused by a number of factors. Please see the list below and ensure that all are correct.

Path to Sendmail is Correct
Please ensure that you have entered the proper path to sendmail within the program's options and that there is a " -t" at the end of the path.

Template Permissions are Correct
Ensure that all templates and the folders containing them are CHMOD 777. If you need help setting permissions, please see this article.