404 turned into 406

I went to schedule my blog for this evening but was struck by a 404 error. By doing some googling and trying to fix it using htaccess files I still havent fixed it, for now im getting a different error. Its now saying 406 not acceptable when trying to post.

‘Not Acceptable

An appropriate representation of the requested resource /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.’

But its only with certain posts. My full post at around 950 words gives me the 406 error. But if I quickly do another entry with one line then it posts fine.