I am getting the attached error when running the installer as a user that does not have local administrative rights. It does not seem to matter though.
Most likely you installed Scrivener with Admin rights, but uninstalled it as a regular user. The error message reports that some registry keys cannot be cleaned due to missing proper access rights.
No, this happened during the first installation of Scrivener on this machine, which I ran as a non-administrator user only. But it does not seem to affect the functionality, only a bit confusing.