It depends which channel you're trying to view.
The keys expired message does appear when the Cam is Auto Updating the keys, for Digi TV, Premiere and Polsat, all channels using Nagra 2 encryption, this unitially takes 5-10 minutes then once the keys have updated you can view the channels as normal.
When switching between channels, especially different packages, the Cam does occasionally lock up, but by simply removing and re-inserting the cam it starts working again.
Please post more details of the channels you're trying to view, and check in the cams menu, configuration folder, that you have N2 AU and Emulators both turned ON.