Your Windows XP Security event log contains an entry similar to:

<b>Event ID: 537
Source: Security
Type: Failure
Audit Category: Logon/Logoff
Computer: <ComputerName>
Logon Failure:
Reason: An error occurred during logon
User Name: <UserName>
Domain: <DomainName>
Logon Type: 11
Logon Process: User32
Authentication Package: Negotiate
Workstation Name: <ComputerName>
Status code: 0xC000005E
Substatus code: 0x0</b>
This behavior will occur if there are no available domain controllers (Status Code 0xC000005E) and the Interactive logon: Number of previous logons to cache (in case domain controller is not available) policy is set to 0.

If no domain controllers are available, you can You can safely ignore this event, you can safely ignore this event.

NOTE: See tip 7134 ยป The Windows XP SP1 and Windows Server 2003 help topic for 'Interactive logon: Number of previous logons to cache' is incorrect?