Ahahhhh! That is why every single Windows 7 update since last October has failed on my machine with two installation trials and endless rollbacks! That explains a lot.

This may be kind of off-topic, but does anybody happen to have a link to some explanation of how to fix this without annoying things like unplugging internal drives or fiddling around with potentially dangerous disk tools? I've looked on official Microsoft community websites but they only give fairly useless advice like switching off all antivirus programs and reinstalling the whole OS from scratch.