Upload Crashing Browser

Hi There
Whenever user try to upload the following happens;

They get a domain user login prompt,
The file begins uploading in the background,
The browser then locks up and you have to force a close of the browser,
The file DOES NOT upload.

I have tried to resolve this but to no avail, I have asked users to enter their login details as DOMAIN\Username and it still does this.

This error is happening both on our LAN and via our WAN.

Help! This is rather urgent as I have remote users needing to get files sent in which are too large to email.

Please see Mac upload error using AD account.

Excellent! That worked a treat, thanks very much Cem