Apparently, the Nikon D4s is having difficulties working together with some Lexar Pro CF cards. Nikon Rumors reported about this a couple of days ago, and now Nikon has released an official service advisory on the issue. The cards causing problems are from two batches with specific serial numbers, and in order to find out whether your card is affected, all you have to do is look at the serial number on the bottom of the card.
The two batches in question have the sequences 8BAFBE and 8DCB61 at the end of their serial number. According to Nikons service advisory, only 400x and 1000x speed cards are affected, although in Nikon Rumor’s original facebook post that we linked to above, a 600x card is also mentioned. If you’re using a Nikon D4s with a Lexar Pro CF card, best take a look if it’s from one of the batches, and if it is, have it replace anyway, even if it’s not causing you any trouble (yet.) Better safe than sorry, and all the more when your income depends on it.