Error 404 when trying to save posts…..

I keep gtting an error 404 when I try to save posts. The message is:-

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Not Acceptable

An appropriate representation of the requested resource /blog/wp-admin/post.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
Powered By BODHOST Server at fu******ers.co.uk Port 80

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I have searched my files to see if the folder is there and it is. I took a look at the permissions, and they are 644, could that be why I keep getting the error?

Does anybody have any ideas why this should be happening?

John