Cannot Publish or Save Posts Properly

There seems to be a problem ever since I used the Beta-1 of WordPress 2.0 till the latest version. Everytime I try and publish or save a post after editing, it would force me to either download the “post.php” file in Firefox or show a blank page in Internet Explorer.

I have deactivated all my plugins and even deleted and reinstalled WordPress over again and the problem is still there.

Does anyone else have the same problems? It can’e even publish my trackbacks because of this.