After uninstalling, I still get the popup message stating that I need to registerThat probably means the SwitchResX Daemon is still running, even after the uninstaller put it in the Trash.
Check with Activity Monitor if "SwitchResX Daemon" is running. If yes, kill it.
Also check in System Preferences -> Accounts -> Login if it's not also launched from there. If yes, remove it, otherwise it will come back after restart !