“Stop: c000021a {Fatal System Error}
The initial session process or system process terminated unexpectedly with a status of 0×000000000 (some more hex codes)”

Can’t repair this. Trying to pinpoint source of problem.

System Restore through Repair Environment is failing. Replacing registry files with those from RegBack hasn’t helped.

Clean install of Vista, moved contents of system32\config from broken install to clean one, also moved old Users directory, and problem still exhibited. Must be a registry/configuration issue then, not system files.

Now going to try to see if I can pin it down to either System registry or Software.

Update: It is fixed. The problem was within the SOFTWARE hive. I moved all the clean install stuff (Windows , Program Files, Users, ProgramData) to a folder called “clean”, and move all the folders out of Windows.old back into C:\ , so in effect returning the machine back to its original state before the clean install. I then replaced SOFTWARE with SOFTWARE.OLD and all is well.

Something within the Software registry hive was wrong/broken. Hope this helps someone. Not sure why the SOFTWARE hive out of RegBack was no good.

At least we know from now on that troubleshooting “Stop: c000021a {Fatal System Error}, the initial session process or system process terminated unexpectedly.” should be done from within HLKM\Software of the registry, or just replacing the Software hive with a good backup. Earlier in the process I opened regedit from the Repair Environment’s command prompt, and loaded the Software Hive, but it looked bare. There were only Microsoft subkeys, nothing else. Either this is because of the fault, or perhaps it’s a Vista security feature? (no.. it’s not a security feature – see below):

Another update: I have taken the bad software hive, and the good working one (software.old), and loaded them up into Regedit on my XP machine to compare.

Both files are around 45mb, but the bad one is completely bare except for a couple of Microsoft subkeys. I wonder what caused this?

Perhaps I am barking up the wrong tree. Maybe the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Reliability\Srt key means “system restore”, and this bare registry is normal during a system restore. Perhaps the registry is supposed to be bare until System Restore finishes after the reboot, and the bare registry wasn’t the actual cause of the stop error. Perhaps the stop error was triggered during System Restore’s finishing up. Who knows. I suppose I could create a restore point on the machine now, and see if System Restore causes the Stop error to return. I might do that.

At least for now, the solution here was to replace software with software.old.