Error Message: The Files can't be sent to <...>: it is required to upgrade Remote Desktop on computer <...> to a newer version.
QuickSupport Version: 2.4.0.48_net4.5.1
RemoteDesktop Version: 2.4.1.19_net4.5.1
Both downloaded yesterday.

David, thanks for the quick reply. I had installed RemoteDesktop as a test, but exactly the same version (download from yesterday), at the time of starting QuickSupport the application was then uninstalled.