Media Center missing TV multiplexes

I have just upgraded to Vista and seem to have lost Multiplexes 1 and 2 (BBC
and ITV) from my USB Freeview receiver (V-Gear MobiDTV). On my Laptop, using
the same receiver, running XP and the original bundled software (ArcSoft
Total Media 2.0.4.69) all mutiplexes are received with maximum signal
stength. On my Desktop (Vista and Media Center) the scan finds all the
channels, but when I select channels from Multiplex 1 or 2, I get "No
signal". The bundled software is not compatible with Vista.

I am using a wideband high gain aerial and live within sight of the
transmitter mast. On the laptop, a tiny room aerial gives an adequate signal
for most channels. I have seem plenty of reports of similar problems, though
not many solutions. The solutions seem to suggest it is a hardware or signal
strength problem, but these symptoms seem to suggest some software cause. I
can't see why the signal level required should depend on the software used.
Using a TV set top box suggests that the signal for multiplex 1 that I
cannot receive is stronger than the signal for multiplex A which I can.

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