Leica has now released a firmware update that resolves the problem with Sandisk cards, as previously reported here: M9 Failure.
Leica said: "With that firmware update, we revoke the constrictions made with respect to the compatible cards. Generally speaking, the Leica M9/M9-P is compatible with any SD card that is in accordance with the respective standards. Unfortunately, it is impossible to test the compatibility of every single card of every single supplier.
All cards available from SanDisk have been compatibility-tested and the firmware version 1.1.76 ensures their proper function."