Restored database from a machine with current version of EM Client to a W10 machine with older version of EM Client.
Started EM Client, responded Update to the Update EM Client or Exit popup.
Okay to the msi installer, the UAC prompt was long time coming - even after CTRL_ALT_DEL and Task Manager. Hourglass on the taskbar, everything a little sluggish, fine after okaying the UAC for the msi. However, the install would not proceed after a popup message indicating an old version was already installed.
Quitting, and downloading EM Client from the site, everything is fine. 
Thanks.