When a user here tries to upload a video to youtube they get a dialog (login) box appearing at the point when the upload reaches 100%. The title of the dialogue box is actually the ip address of the proxy (smoothwall) server and its asking for a username and password (standard windows popup dialogue)

As this is happening, in the proxy logs I see a repeating 404 error for the youtube page:
http://upload.youtube.com/api/upload_feedback?id=blah blah blah

These 404 messages continue until the diagog box is cancelled. if you try and enter a valid username it just seems to freeze the page at that point.

Very bizarre behaviour - anyone seen anything like this? We don'tblock youtube at all (for staff anyway!)