I'm not sure about blocking it, however a way that might would be to look for a setting which disables it all together or puts the machine into a manual mode, i.e. you choose as and when to scan for new channels not the machine.
Is it definetely the DVD recorder and not the TV that's displaying the message (I'm sure you've checked but thought I'd ask).
I'll see if I can paw through the hefty manual later on if you don't find a solution in the meantime.
I think this is one of those problems that you eventually stumble upon the remedy when you least expect it. I can't help much further than that I'm afraid without coming round to your house and sitting in front of it for a while, and that's simply not possible.
My only other suggestion would be to give Panasonic a ring in the morning.