I cannot remove old ActiveX/COM entries.

Do you have any programs that stop program from editing the registry for security reasons (i.e. any good security program with real time scanning/watching). Did you try going directly into the directory finding the keys and deleting them (WARNING: If you don't have experience with the registry and don't know what most things are in it, do NOT try this.)

I checked a few of my backups, and I see that I have a couple that have 'returned' as well. This is usually because applications you still have installed restore the registry keys, either at boot, or when launched.

It is nothing to worry about

I just came across this article by DjLizard, and in this case it could indeed be a Permissions issue as well.

Have a look.