Outlook prompts for network password (not ISP password)

I run (to use the term loosely) a Win2kPro network using Office XP. One client is having a problem with Outlook. When he opens the program, he is prompted for a network password (username and domain are filled in). He enters his password and proceeds as usual. Where might this "prompt for password at startup" setting be? I've looked at all the profile settings I can think of and can't find anything. In his settings, his Outlook is set to always use his profile. Any suggestions?

 

It has been awhile since I have used Outlook, but I believe you have to get into MS exchanger server. Look in Control panel, mail.