I am running SBS 2011 with about 20 clients. 2 of them are having this issue.
The clients with the issue are XP sp3 with office 2007 sp 3. (the rest are a mix of xp, vista and 7, with office 2007 and 2010) When outlook opens up it connects just fine. However, when I try to create a calendar item Outlook prompts for username and password, saying it is disconnected from the server. However, mail is received and sendable. I have been trying everything. I suspect it is the outlook anywhere that is asking for the credentials. Both connect with Http boxes are unchecked. I have tried all of the combinations as well.