The 500 error is an error generated by the server when it encounters an error condition that can not resolve automatically. That is, if a file is not found, the error is 404 (Not found), if you can not lists a directory, the error 403 will be launched (Forbidden). For errors that do not have an explicit definition, will raise the error 500 (Internal error).
This error usually occurs in Apache:
when used in the .htaccess file some unsupported directives.
in some hostings…