Error: Failing to Post – any help greatly appreciated :)

Hey Guys

Since the WordPress upgrade to 3.1.1 and 3.1.2 by WordPress sites are not letting me add new posts and keep giving me the following error message:

“Error 404 – Not Found

Sorry, but you are looking for something that isn’t here.”

I tried disabling all plug-ins but still get the same error.

Any ideas on what may be causing this or how it could be fixed?

I really appreciate any suggestions you have to offer ??

Jamie