When I install 9.1.1.8, I get the attached or a similar message during the reboot requested by the install.
I post this for information. So far, I'm not aware of any continuing ill effects after this message.
I've seen that as well. Seems to only happen on XP for me, not on Vista. I think it's safe to ignore -- at least I've never seen anything go wrong after that error -- and it's probably just Install Shield trying to clean itself up when it's already been cleaned up.