Spooky I am having exactly this problem. I have a few suggestion which may help. Firstly install the ISA service pack 1 released this month. Also check that your clients are using at least IE6 or IE5.5 SP1 as lower versions can give you this problem. On the ISA server managment console go into the properties of your ISA server and set the authenitcation to basic. There is a Q article Q198116 which desribes this problem on Proxy 2. I hope some of this helps, I am still working on our problem here but as soon as I have an answer I will let you know. Liz Milne MCSE