Whenever I am troubleshooting a web problem, I keep a separate terminal window open and 'tail -f error.log' for the apache error log. It usually makes quick work of tracking down where a problem lies, especially since most browsers aren't giving useful error messages directly to the browser.

Also, it's a great help if you post some code (using the <code> tag) so we can better assist in finding the problem. If the code isn't too long, I'd recommend posting the entire thing, so someone can just copy/paste the entire script into their own system and try to run it (obviously having uncommon dependencies may hinder this) but it's good to get an overall idea of what you're trying to do, and what is actually happening.