Here's a fun one:
A client of mine checks her email through owa. When she replies to an email on any of her 3 windows xp machines at her house, when she clicks send the buttons grey out and it sits for a while, then a MS IE popup window opens with a yellow exlamation point and the text "Unknown" and the option of OK. After you click ok, the message appears as a saved draft (same thing happens again when you try to send from there). Also it doesn't do attachments, buttons grey out and nothing happens when you try to attach.
I have tried updating windows completely, including optional .NET updates. I have disabled norton internet security. Double checked all settings. Lowered all security settings, added the site to trusted zones, no change.
Any help is appreciated