sudden error when trying to post

I just began getting this error when trying to post…instead of showing the regular WP screen that comes up after sumbit a blank page comes up with this:

http://www.divaknitting.com/blog/wp-admin/post.php 65.29.203.219 /blog/wp-admin/post.php http://www.divaknitting.com Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322; Media Center PC 4.0) 403

Any ideas as to what might be happening?