This is actually the strangest problem of my existence, and should not even Google it. It's happening with an Apache powered website designed in PHP, which utilizes mod_rewrite (but that is not the problem, I attempted getting rid of the .htaccess file, problem still is available).

If I've got a query string that appears exactly or much like: =/id I recieve an 501 response:

Method Not Implemented

Reach / not supported.

Furthermore, a 404 Not Found error was experienced while attempting to make use of an ErrorDocument to handle request.

I never written such error page, never sent an 501 response, not have the smallest clue where this factor is originating from. Initially I'd a lengthy URL giving us a similar error, however i removed lower for this little snippet above. Basically remove or change any character, the error's gone.

In the event that helps: this site is commentards.net, and also the original URL was an openid login request which appears like this:

http://commentards.net/q/user/auth?openid_identifier=https://www.google.com/accounts/o8/id

that the query string is:

?openid_identifier=https://www.google.com/accounts/o8/Fid

I requested the support team, plus they stated it had been mod_security, and disabled it for this site. And today it really works fine. I ought to have began with this. Anyway, interesting help.

Maybe should you take away the error you receive with no GET parameter first http://commentards.net/q/user/auth

After which urlencode your query http://commentards.net/q/user/auth?openid_identifier=https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2Fid

Urlencode your query string parameter(s).

https://www.google.com/accounts/o8/id becomes https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2FFid

http://commentards.net/q/user/auth?openid_identifier=https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2FFid works fine, so HerrSerker already clarified your question.