Leica has just released a new firmware update, Version 1.174 which is now available for M9 and M9-P cameras. It fixes compatibility issues some M-9 owners had related to select types of new memory cards.
However until further notice, the following SD-Cards are still not recommended:
San Disk Extreme Pro SDHC I UHS-1 (all card sizes)
San Disk Extreme HD Video SDHC I (all card sizes)
You can download the firmware here :