registry key in HLM\system

Windows won't let you because it's not a good idea. If you succeed you'll end up crashing your OS. DO NOT DELETE!

Windows does not allow simultaneous deleting of multiple registry keys.
If you are set on deleting these keys I would make an export of them before hand, and make sure that you have an up to date recovery disk.
Since these keys control how Windows handles drivers & applications created for previous versions of the OS it would be wise to leave them alone.

You can delete them one at a time, time consuming task.
If you do decide to delete these keys make a restore point with system restore then, if the system locks up or operates unstablly, you can restore the system to the state before you deleted these keys.
ALWAYS make a backup of the registery BEFORE attempting ANY changes.

Deleting of such a LEGACY key is not normally possible. I want to get rid of corpses in the registry! - HOW ??

Have you tried exporting HLM/system and then right click on the exported file and pick edit. You can then delete to your hearts content and then import it back into the registry? Just make sure you have made a restore point, a backup of the registry and you have a bootable CD or floppy so you can repair the registry if the computer will not boot after doing this. Have you tried using a registry cleaner to do this? Good Luck.

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