Cannot logon interactively

Scenario:

Windows XP Pro;
Standalone, never joined in a domain; but plugged into client’s intranet occasionally;
Shutdown normally the night before when standalone;

Now the problem is:
The second morning, at the client?s site, plugged in the network cable, and then turned on the machine. Suddenly, I could not log in locally. The message is: “The local policy of this system does not permit you to logon interactively”. No matter which valid local user account I used, I was rejected by this message.

Please advise. Thanks.