Thanks for your question. Cards were NOT taken from a Canon and placed into a Nikon without first attempting to format in the Nikon. (Been doing this a couple of decades now, ahem...) But that is indeed a good point to be heeded by newbies. I bought two other brand new cards in the store and NEITHER OF THEM would format in the D800 except my Sandisk Extreme IVs. I have enough experience under my belt to have been caught in situations where the cards I brought along were lost/stolen and I had to use what ever I could get my hands on. I have probably taken it for granted that my cameras so far have never had CF card issues. Today, that is something that should be taken for granted if anything is. The main point is that we should not even be having this discussion in 2012 - and particularly not about a $3000.00 camera from Nikon. I cannot trust it. Would you take an exotic new car that wouldn't start all the time on an important trip? Or would you hop in something that you knew was going to get you there?
What brand were the Cards?
While almost all cards work with it, some will not. Some Delkin, Dane-Elect, Kingston, and "My digital Discount" have been reported as not working, http://www.robgalbraith.com/bins/camera_wb_multi_page.asp?cid=6007-12451
I have a whole pile of CF cards, I usually use Sandisk Extreme 60 mb/sec, but I also tried a older Lexar Professional 300X, A really old "Lead Data" 8MB", a really old Sandisk 512MB, a old Transcend 8GB 133X, a old Lexar Pro 4GB 300X. I could likely dig out more from my junk box out in my studio, but we are in the middle of a thunder storm and I'm staying dry.
Only the old 8MB (MB, not GB) card would not format, but it did not lockup the camera either. Obviously, it could not store even one image in any event.
The rest of the cards I tried formatted perfectly, and I took images with them as part of testing. The camera took everything I could throw at it, the same as my 5D MK III did.
It works fine with my SD cards as well.
On the other hand, the 5D MK III worked with all of them! http://www.robgalbraith.com/bins/camera_wb_multi_page.asp?cid=6007-12452