Hi Peter -
I checked the logs and FSUIPC was quite happy with the MRAI Trafficboard's attempt to connect with it. Even so, no traffic info was being captured. I tried to revert to an earlier version of FSUIPC but, because I have the Flight Simulator patch, that wasn't possible.
What I'd not done was upgrade the Trafficboard to version 2.1 from 2.0 - I'd already d/l-ed the latest version of the Trafficboard but hadn't installed it. Once I'd done that, everything started to appear once again.
I expect the Trafficboard V2.0 had the problem - since all three elements in the equation, FS9.1, FSUIPC and the MRAI Board have had recent changes it may difficult to figure precisely why. The upgrade of the Trafficboard from 2.0 to 2.1 doesn't appear to have addressed this issue (not according to the modification history), but either way it appears to have fixed it, which I suppose means I'm the only person who noticed. Either way the problem seems to have quietly slipped away.