REGISTRY_ERROR in XP

A customer’s computer running XP Home runs into a blue screen every way I try to boot it, including Safe Mode. The error is REGISTRY_ERROR, STOP 0x00000015. If I boot from a CD, and go into the Recovery Console, the minute the computer logs onto the Windows installation on the hard disk, the blue screen returns. Likewise when I tried to do a repair installation. I examined the hard disk independently, and it seems to be okay. Any ideas what this might be?
I am not sure if SP2 was installed, but the original installation was SP1a.