406 Not Acceptable Error

I know this sounds like a server side error message, but I only get this under one circumstance:

Under Manage/Posts, and after I click the “save” button, I’ll see this message. The edited post will be saved, but I just have to use the browser back button to go back. After I go back, I only see the unedited version of the post, even though the post is updated on the live site.

I’ve never encountered this problem before. On the same server I have another WordPress 2.3 blog, and it doesn’t have that problem.

The exact message reads:

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