Have your heard of that? This was a case about an user that was getting his account locked out in AD every time that he connected through Outlook Anywhere. As usual until get to this conclusion we had to pass through painful troubleshooting steps. Starting from the Troubleshooting Account Lockout approach to narrow it down that the issue was happening only when using Outlook Anywhere through ISA Server. Here the explanation of the issue:
An Outlook Anywhere client continually uses the wrong credentials every time that it tries to authenticate itself on an Exchange server after you install ISA Server 2006 Service Pack 1
Wants to fix that? Make sure to update your ISA Server 2006 SP1 with the Post SP1 update (July 2008 Package).