Getting output like this on occasion:

Forbidden

You don't have permission to access /forums/showthread.php on this server.
End of script output before headers: showthread.php

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.

Apache/2.4.18 (Unix) OpenSSL/1.0.1e-fips mod_bwlimited/1.4 Server at driveviper.com Port 80

Hitting refresh a couple of times usually fixes it.