My users just started getting prompted for credentials in the last couple of days. Most users are using Outlook 2007. We have a server in site "A" Exchange 2007 SP3 all roles and two servers in site "B" Exchange 2007 SP3 one with CAS role and one with the other roles. Only the users with a mailbox in site "A" are getting prompted, no matter if they access it from site A or B. Also users with a mailbox in site B, accessing it from site A are fine. I created a new mailbox in site A and I am getting the issue also. From site B if I access a mailbox on site B I am fine, but if I access a mailbox on site A I get the promts every couple of minutes. I don't see any relavent error messages in the event viewer on the WS, AD Controllers or Exchange servers.