500 Internal Server Errors are caused by errors on your account that you can easily fix once you figure out what the error is. The common causes for 500 Internal Server Errors are below:
1. Permissions. Files MUST be 644 and folders MUST be 755.
2. Not specifying a RewriteBase when using RewriteRules in .htaccess.
3. Trying to use php_flag or php_value in .htaccess.