OK I think I have got to the bottom of the problem.
Both my LG37" TV's have DVI-D interfaces. I have a DVI to HMDI cable on both units.
When I plugged one of my units into one of those new Samsung LED TV's using a straight through HDMI cable it worked perfectly.
So whatever Buffalo did in the last firmware update, broke the compatibility with the older HDMI/DVI interface.
Also (PerryM) I checked with LG and the TV's I have both support HDCP, although from reading through other forums this can also be problematic.
Anyway, I am connected to the rather grizzly composite output now, and hoping that Buffalo will fix the problem. I couldn't sell my wife on the 2 new TV's idea because of an incompatible firmware update, she wants to know why we can't go back to the old release which worked fine.