Remember my series of columns on the mysterious outbreak of deferred procedure calls that randomly occurred on one of my Windows XP machines? Just to refresh your memory, DPCs are Windows system calls that are deferred so the processor doesn't get tied up with work that isn’t immediately required. A more techie description can be found on Wikipedia.

Out of nowhere the processor utilization caused by DPCs on my box jumped from a few percent to 40%-50%, turning my PC into a very attractive boat anchor. The question was, why? What was causing this to happen? I never found an answer, and as mysteriously as the problem arrived it vanished.

While I was wrestling with the problem y'all suggested all sorts of potential causes, including faulty hardware (couldn't find anything and I hadn't changed anything), a misbehaving driver (why would one suddenly start causing problems and then stop?) and bad ju-ju. The last may be the best explanation of all.

I had several culprits of my own in mind, the most compelling being Microsoft's automatic update service, but the problem vanished before I could find any solid proof.

Reader Gary Lavery recently wrote to tell me about a similar mysterious problem where something was chewing up cycles on his PC, but unlike my DPC problem, Gary seems to have identified his gremlin.

Gary says that periodically his machine (a Dell Inspiron e9400 laptop with XP Pro and 2 GB RAM) would freeze and the disk light would go on solid for 30 to 60 seconds.

To find out what was up Gary turned to Glint System Monitor, a freeware stay-on-top system monitor. Glint showed disk reads were the problem, but what process was responsible? For that he turned to Microsoft's freeware FileMon for Windows: that "showed unbelievable open, query, close cycles on WCESCOMM.LOG."

Not knowing what this file was, Gary searched Google and found it belongs to Microsoft's ActiveSync. "Ah ha!," he says. "I had installed [ActiveSync] to sync my phone remotely a long time ago, but it doesn't work when Outlook is hooked up over a VPN."

So Gary used the freeware Revo Uninstaller to remove ActiveSync and voilà! His PC immediately started to behave itself.

Now Glint "showed very little activity, whereas it had been lit up like a Christmas tree previously," Gary says. "Filemon also showed very little activity, where before it had been overwhelmed with open, query, close cycles. These symptoms sounded similar to what you described for deferred procedure calls."