501 Method Not Implemented when updating System info

I installed Opencart 1.5.6.4 along with a Template Monster template at domain http://www.linen-and-lavender.com

I wanted to *temporarily* lift the "Maintenance Mode", so I could test the responsive template with a mobile phone emulator. When I attempted to change the Maintenance Mode setting (under the System -> Settings -> Server tab), and then tried to save my change, I received the infamous:

Method Not Implemented

GET to /admin/index.php not supported.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

message. I have only seen this message referenced in the forum in the context of email settings. Is it possible that the error is still due to an email issue, even though I made no changes to the email setting since initial installation?

[Edit]

I tried to change the email settings from "Mail" to the SMTP settings for the server (to eliminate MAIL as a possible cause). The error was still generated.

is this issue has been fixed?