No, that’s not normal.
Have you tried unplugging the box from the mains and then plugging it back in again?
Also reinserting the card might convince it that there is actually a card in.
Not that it really matters if everything else works, but it might be the sign of a software fault on your box, if it still doesn’t give a card number you could try a software upgrade (but beware of loosing recordings when doing that).