My b2evolution Version: 2.x

Hi

I've tried using a couple of skins, including the default skins but the problem is arising in all. When I try to submit a comment on any of the post, no matter I'm logged in or not, it returns an invalid page after clicking on submit or preview button.

Although, the comment gets posted, when I see that in the admin or by re-opening the post from the start, the comment appears there. However, if you write a comment and post, the next page that returns is an invalid page and displays this message:

400 Error - Bad Request
The purpose of this message is to inform you that your request for service on the server could not be completed due to malformed information on the part of you, the user, or your client program. Please verify your request and try again.

Can you please go to http://www.mygrants.us/blog and try posting a comment there. The comment gets posted however, it doesn't redirect the user back to the article page, where the user can view his posted comment. Please let me know how to fix this. Thanks.