I've searched the solutions here and found a similar, if not exact match to my problem in Q_20732632. I've reviewed and re-reviewed this solution and the referenced MS KB articles. I've followed, carefully, the MS KB directions for setting permissions. Yet my problem persists.
I have two servers in the environment. Server1 is running 2000sp4, AD, and Exchange 2003. I know, not recommended, but our only option. Server2 is running 2000sp4, MS Proxy 2.0. I'm running only a single SMTP domain.
Most accounts in my exchange environment are prompted 4-5 times for their logon information. After the last prompt, the users are presented with a 4.01 error. If they refresh the browser the inbox/account is displayed properly. I say most accounts because my account works fine (admin level permissions) as to a small number of other accounts. The other kicker is that accounts that prompt multiple times when accessed via the LAN logon fine from outside the LAN on the public internet.
This issue has been on going for a long time. Your thoughts, time, effort, and suggestions are all appreciated.