February 2016
The fact uninstalling is telling you that an EP is still installed suggests that you have files/registry entries still on your machine after you uninstall the pack(s).
Does it say which packs it thinks are still installed?
As you say you aren't using Origin, that means you are running 1.6.7 Super Patch and not the new 1.6.9 version that Origin has, correct?
February 2016
No, the notification gives no information as to which EP it thinks is installed, but I have a sneaking suspicion that it's Generations, because I had it installed last time I played the game, but was unable to find the disk to install it now. I think that since I can't install and uninstall Generations like I can my other EPs, all the uninstalling I'm doing now won't affect any leftover files from Generations. However, like I said in one of my previous posts, I've followed the complete uninstall guide on the Sims wiki at least twice now, so either I've repeatedly missed a registry key listed in the guide during cleanup, or the guide is incomplete.
Yes, I am using the 1.67 super patch. I've been wanting to try an earlier version of the super patch such as 1.66, but the EA download site fails to finish any attempted downloads for me.