I am having the same problem. I have a brand new computer, in fact I have two Windows 10 machines.
I purchased start10 last night and on either machine it has error message "Please Reboot to complete the Start10 uninstall before proceeding with the new installation"
Start10 has never been on either computer. Rebooting does not resolve it, and one of the computers is fresh out of the box and has all windwos updates.
I would like my money back if this can not be fixed shortly.