After install, can't access any admin pages

I recently attempted to install Node Access but I end up with a pretty serious problem in that I can't access any admin pages once it's installed. I ran update.php to see if that helped, but no luck -- everything either times out or responds with a 500 server error. The only fix is deleting the module and rerunning update.php.

Interestingly, I have the same problem when trying to use Content Access. I'm running on a Network Solutions server, if that matters.