La verdad es que como recomendacion te puedo decir que pongas en google error 500 y leer es una buena practica en estos casos.
Si quieres ayuda del foro te recomiendo dejar mas informacion acerca que, donde y como (hablo acerca de codigo y no tienes que dar el codigo pero si una descripcion para tener una idea).
Te dejo un copy paste de algo que quizas te resuelva tu duda y si no te recomiendo usar "google" es tu mejor amigo.
Fixing 500 Internal Server Error Problems on Your Own Site
A 500 Internal Server Error on your own website requires a completely different course of action. As I mentioned above, most 500 errors are server-side errors, meaning it's likely your problem to fix if it's your website.
There are lots of reasons why your site might be serving a 500 Error to your users, but two are most common:
A Permissions Error. In most cases, a 500 Internal Server Error is due to an incorrect permission on one or more files or folders. In most of those cases, an incorrect permission on a PHP and CGI script is to blame. These should usually be set at 0775 (-rwxr-xr-x).
A PHP Timeout. If your script connects to external resources and those resources timeout, an HTTP 500 error can occur. Timeout rules, or better error handling in your script, should help if this is the cause of the 500 error.
A Coding Error in .htaccess. While not as common, be sure to check that your site's .htaccess file is properly structured.
