406 error when trying to publish a new blog post

I’m getting the following error message, when I’m trying to put up a new post:

“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.”

I have tried clearing the cache, rebooting my computer and modem, and also posting from two other computers and internet connections. I have also tried to reinstall WordPress, without success.
There were two external links that I thought could be the culprits, but I’m getting the same error.
Any help or direction would be welcome! Thanks!