Forum Error Message on 82-page threads

[محروم.كوم]

Upgraded last week and everything was fine for a few days. Now we're experiencing a host of bizarre problems.

Why would the last page of several 82-page threads suddenly be inaccessible, with the following message?

Forbidden

You don't have permission to access /showthread.php on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Apache/2.2.15 (Unix) mod_ssl/2.2.15 OpenSSL/0.9.8m DAV/2 mod_fcgid/2.3.5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 Server at www.thewritingbridge.org Port 80 __DEFINE_LIKE_SHARE__