Crazy problem: controllers don't load

[eluser]bradym[/eluser]
Have you turned on logging to the highest threshold to see if any messages show up in the log? Also, what are you doing for 404 errors? Are you redirecting them? Have you checked your .htaccess to make sure you don't have any redirects you don't want?

I've never seen the behavior you're describing, but these things are what I would check first.