the 500 server error is a very vague error that literally means "An error occurred" many hosts will display this error and hide the real error message. We need to know what the real error message is.
when you see the error, make not of the page in the address of the address bar.
on that page, you can add the following code at line 1 to turn error reporting on:
if that does not show the real error, you will need to contact the host to have them look into the error logs.
once we know the real error, we can begin troubleshooting the cause.