Causes of internal server error 500

My server seems to be b0rked with a 500 error. What kind of things cause this?

Check your error log and you will see.

Usually it is a typo on the coder's part...missing brackets, expected brackets, malformed code, doing things in the wrong order, semi-colons, not enclosing a string with what you opened it with, not escaping special characters, etc...but your error log, if you have access to it, will save you over and over again. Also, if you hosts as it enabled, you can just login through SSH or telent and do ./filename.ext to debug it...

It must have been my .htaccess, this line:

RewriteCond %{HTTP_USER_AGENT} ^Cold Fusion 4.0.*$

presumably the "4.0" part.

mod_rewrite doesn't like blank spaces in the user agent you are checking for, so just use this

RewriteCond %{HTTP_USER_AGENT} ^Cold [OR]

Leave off the [OR] if you aren't doing multiple checks