Before installing an updated version of the Visio add-in, please close Visio and de-install the existing installation add-in in the Windows Control Panel. You can also check in Visio if the add-in is no longer visible in the list of installed add-ins (go to File / Options / Add-Ins / Manage: Com-Add-Ins).

After that, proceed with setting up the new version of the add-in (please ensure that Visio is closed while running the setup program).