Just recently some of our users reported a password prompt box in Outlook repeatedly coming up. After testing I determined this was only occurring while inside our network (Outlook over HTTP), not while connected through OA. We are on Exchange 2010 with mixed Outlook 2007/2010 clients on Windows 7. This issue is occurring with less than 10 percent of our 750 users, and I can't find a common attribute between them that others in the org don't share. If we login to a computer with an affected account on a clean Windows 7 install, the issue persists. Our Exchange install has been up and running for many years without this issue and there were no changes/updates made recently. It seems like the prompt comes up when Outlook attempts to connect to OAB. I've checked OAB file/folder permissions and all are correct according to MS guidelines. I've rebuilt OAB and restarted the server. Can someone please point me in which direction I should take next for troubleshooting?