Hi,
A lot of forums describes this error like being a webserver problem. So the problem is not in AwareIM, it's on your web hosting server.
"even if you are using IIS or apache, my guess you are using static html page as a landing page, and by default the web server doesn't allow POST or GET verb on .html page.
the solution would be to rename the page into .php or .aspx and you should be good to go"