1) Recreated Outlook profile
2) Unjoined and rejoined PC to the domain
3) Recreated desktop profile
4) Updated NIC driver
5) Removed and added server entries under Control Panel\User Accounts\Advanced\Manage Passwords
6) Installed Microsoft hotfix - article ID: 885887
7) Verified PC is getting DNS servers from DHCP and no manual entries.

9) Verified Client for Microsoft Networks under TCIP/IP properties
10) Reinstalled XP Service Pack 2
11) Changed Outlook authentication to NTLM
12) Verified NIC speed/duplex setting is the same as the port on the switch
13) Scanned virus and spyware, and the PC was clean
14) Renamed his computer
We tried all these stuff and no luck. He will still get the same pop-up, Outlook gets disconnected and AD account gets locked out. Today, I was doing some tests on his PC. I uninstalled X1 since the problem was Outlook related to see if that would change anything. Rebooted the PC and reinstalled X1. Launched X1 after the installation with Outlook open, Outlook immediately threw me the pop-up box and account in AD got locked out. I unlocked the account and uninstalled X1. I told the user to use the PC without X1 for a few days and see how it goes. I'm suspecting X1 is the culprit. Does anyone have the similiar problem?