Everytime I get an error in any of my PHP, my local Apache server gives me a 500 Internal Server error. I never seem to have problems with any of my CakePHP projects, but this is plain vanilla PHP and it is really slowing down progress having to guess at the error.
Enable error reporting using the following PHP code:
What @scompt wrote + you can always check the Apache error logs to know what happened. (hell, if you develop on linux, host on Linux, you must be familiar with the error logs).