I got this when I turned on my machine this morning. What a shocker. I booted the restore disks, and repaired the OS selector, and reactivated it, and all is well. But what caused this in the first place? I defragmented my C drive yesterday, and this was the first reboot since then. Anyone run into this before. I have no errors on my drives that I'm aware of. Chkdsk finds none anyhow. Win XP Pro SP2.