Same irritating problem here fixed with the msi cleanup tool.
This tool however is no longer available at the link in the post above it has been removed by Microsoft.
I found several places the tool is available and used this link at softpedia
http://www.softpedia.com/get/Security/S ... lity.shtmlBecause it is the least prone to misleading spam links and unwanted downloads - cnet is dire these days.
That worked fine and allowed me to finally upgrade v3.6.2 to v3.8 after a lot of wasted time and aggravation - it also appears to go straight into Windows 8 64 (not the 8.1 version) without issue and run fine.
As a matter of interest I am a system builder and a certified geek, I have recommended / pre / post installed Classic Start (with an exhortation to make a donation probably wasted but I tried) for 90% of my clients who are largely thrilled with classic start (if indeed they notice it - they sure as hell notice the start screen if I leave Win8 as standard). I have also had a number of frustrated and really angry users in some cases cursing me for this uninstallation error / upgrade issue which I can understand, they have better things to do and no clue how to fix it anyway. Even with my experience it has taken a few hours of faffing about(which I am not getting paid for either) to find this fix after trying all sorts of stuff
so ..................................
This issue is out there and affects some percentage of users who are potential donors and probably eventually paying customers, can I suggest that this thread is pinned, clearly labled as a probable fix for the cannot install / upgrade issue and linked on your sourceforge homepage with instructions.
Thanks
Jonah