In rare cases, the .msi installer can fail with the error "The specified account already exists". As far as we can tell, this is not a bug within Canopy's installer but rather with .msi installers in general, where certain registry keys can become corrupted during an install or uninstall.
Microsoft recommends running their fix-up utility and then reattempt the installation. We have found that this has resolved the issue in the few cases we've encountered.
If the Microsoft install cleaner utility is unable to repair the failed install/uninstall, the only remaining option for installing Canopy would be to create a new user account and install Canopy from that user.