401.1 errors about an hour after I restart IIS

HTTP 401.1 - Unauthorized: Logon Failed

start/stop doesn't help. Restart does....for about an hour.
After about an hour I start getting the same error.
Make it go away.

I'm running IIS 5.1 on XP Pro.
Allowing anon access with IIS control password.
read access.

Hi dude,
This problem may be caused by a number of reasons. However, the following are the most common:
• The users credentials (the username and password) are not correct.
• The user account may not have the right to log on to the computer interactively (the "Log On Locally" right). In some scenarios, the user account requires "Log On Locally" right.
Resolution :-
*Reset IIS and see whether things are working fine
*1. Open the Local Security Policy tool from the Administrative Tools folder.
2. Click Local Policies, click User Rights Assignment, and then click the Log On Locally user right.
If the user account or group that the user belongs to is not listed, then add it.
Check out these Articles too :-
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1. 271071 for IIS5
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Thanks,
Jeethu Joseph
IIS/Asp.net Engineer Microsoft