It's a forum. You aren't always going to get answers, let alone timely answers.
I can't help much with the underlying problem, although I will state that as it is an Analogue signal, and WMC is also having trouble, then it is quite possible that the signal strength isn't very good.
However, if you get the "The video capture card is in use by another application" message in MC you should go to;
Options > Television > Advanced > Show status
to see if MC thinks the tuner is in fact in use, or idle.
It could be just that the signal is so low that MC can't find it, so it isn't available and therefore MC assumes it is "in use by another application".