You can try it yourself by going to http://nhacdieu.net and then click on the top-left button (on the red bar).
The link works for me, I think. Can't understand a word it's saying.
I do know I'm not getting any POST request not allowed Apache errors.
also seems to be working for me. I'd sigguest you clear out your cache, and temporary internet files and see if it works for you.
That's after I changed the destination file to php extension insteads of html/htm.
From my research, this is because of the configuration of the server. Anyway, at least change to php extension will work.
Ah, sounds like you were sending a POST request to an HTML file. Which you would get POST request not allowed. You can't send POST requests to HTML files, only GET requests.