Mark Minasi's suggestion to reset the registry fixed this problem for me. As per Mark Minasi: "My XP desktop stopped synchronizing its time with the domain. The Event Log kept showing that the desktop had not time-synced with any of my DCs in weeks. That worried me because if my workstation's time drifted more than five minutes from the domain controllers' time then I would not be able to log on. Once I was three minutes off, I figured it was time to figure out what had happened.
I tried to re-synchronize from the command line:
w32tm /resync
And got "the computer did not resync because no time data was available." Ouch, that does not look good. Then I realized that I had fixed my system's time server as an experiment rather than letting AD set it. Some free time sync programs do that also, so many of you may be in this position. I just cleared out HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\W32Time\Parameters's "NtpServer" value entry, and then I restarted the Windows Time Service. Sadly, no dice ... still no sync. For some reason, if your domain does not find all of the Registry entries to be "just right, " then it will not sync with your system. You can, thankfully, fix it with this command:
w32tm /config /syncfromflags

OMHIER /update
Type that from a command line, and then restart Windows Time Service and retry the w32tm /resync or, better,
w32tm /resync /rediscover
A command that cleans out and rebuilds a few other Registry entries. I had that problem with my XP box about a year ago; since then I have found these commands useful on a number of systems. When workstations get more than five minutes out of sync with the DC, then they stop authenticating but they're not very forthcoming about the reason -- so when authentication's a problem then first look at DNS, and if that doesn't help then look at time!"
See the link to "Mark Minasi Windows Networking Tech Page Issue #34" for the original article.