When a user is logged onto a Windows XP Professional computer as a local user, and that computer is a domain member, logging off posts 2 logon failure events, ID 529.
If you have enabled auditing for logon failures, you will experience these events.
When the user logs off, Windows XP re-reads the user information so it can optimize the next logon. Because the computer is joined to a domain, a bug causes Windows XP to contact the domain, even though the user is logged on with a local SAM account.
You may ignore these errors since they do not cause problems. Microsoft will fix the bug in an upcoming hotfix or service pack.