Installing 4.11.20 (November release) over an existing 4.11.x version will prompt the message:
A more recent version of Scanshare is already installed on this computer
The issue is due to the wrong version number generated during the installer creation in the build number part 4.11.20. This will result in a lower build number than the previous ones 1020, 0920, 0820, 0720 making Windows Installer generating the message.
Uninstall manually the existing version, then run directly the new 4.11.20. Although for Windows Installer the version would be lower the software will be upgraded and all settings and license retained and fully working. With any next new update the software can be upgraded by launching directly the new installer no matter of the version number.