Cable Forum - V+ Smartcard issues?

When I got my TiVo installed, I had my old SA V+ moved into the bedroom. It was fine at first but then the noise of the hard drive started to annoy me at night so I began leaving it unplugged and only re-connecting the power when I wanted to watch something.

The last few times, when I've plugged it in, it's come up with a warning that the Smartcard is invalid. Doing the remove - reinsert doesn't clear it but usually, if I leave the box on sometimes it suddenly decides it's OK after and hour or so. Unfortunately it doesn't always, quite often it says channels I do have in my package aren't subscribed and a few times it won't work at all and I've rung faults who just re-activate it and all is well.

Is something wrong or do cards / boxes get "dropped" off the system if they're not seen online for a while? I sometimes don't plug the V+ in for over a month, but it's really annoying when I do want to watch something and it decides to not work.