For anyone having issues with the x940bt not recognizing their sd cards, try setting the Allocation Unit size to 16kb when formatting. I too had issues all morning trying to get this installed, on several cards as well. I tried setting to 16kb before formatting, transferred files to sd card afterwards, inserted into HU and VIOLA! It worked.
Something to try for others having the same problem with the sd card recognition problems.
Oops...forgot to say the solution that worked was with a 32GB Class 10 card as well.