I think that the card must be stuffed. I tried formatting in the M9, then on the computer, and back to the M9 to no avail. Interestingly, the card in question is an 8 GB Sandisk Ultra (15 MB/s) card. Perhaps the transfer rate is incompatible. Cards which work in the M9 are all of the "cooking" variety. Perhaps the lesson is to stay down market.
Contax IIIa, IIa, Leica M 240, M Mono, MP, X1, DLux 109, Sony A7r, Lumix GH-3.