Finally reverted back to v10, but it took a scrub of the registry to delete all trace of MWP V15, reboot and then install V10. The result is that the Add-on for Outlook works successfully.
Happy for this topic to eventually die.
Meant to say:
Finally reverted back to v10, but it took an uninstall of V15, then a scrub of the registry to delete all trace of MWP V15, reboot and then install V10. The result is that the Add-on for Outlook works successfully.
It may not use the registry, but an uninstall, removal of MWP directory, reboot, install of V10 resulted in the Add-on not working. But it did with a registry scrub. There was probably a Windows 7 issue causing this problem. At any rate I'm that it's fixed.