If you get an "odd" error message, the first thing to do is Google the error. Take out the your-site-specific part (the IP and filename) and try it:
Google: "GET 500 (Internal Server Error)"
Then start by looking at the results you get: they should help you narrow it down to a "reasonable" number of possibilities and the can then ask for specific help with your code.
At the moment, there are far too many possible ways for you to have caused this.