In WordPress Admin, Sometimes Downloads a blank text file

Hi,

Every few weeks or so, when inside the WP admin, trying to upload a photo for a blog post or something similar, my browser gets a notification that the server is sending a file to be downloaded. Most recently my browser was trying to download media-upload.php. When I opened it, it was a blank/empty file.

Usually the only way to fix the problem is to restart Apache and then it works fine for a few more weeks.

Any idea what might be causing it or where to look for a potential problem?

Thanks
CentDev