There is two versions of M92, it's related to the origin (the shop) of the device.
The firmwares in this thread is only for the device ("black" or "white") sold by : http://www.ereader-store.de/
. Booxtor works for this seller.
You could not use this firmware with the "black pearl" sold by : http://artatech.pl/k
. The devices of this vendor are locked. Maurice13 works for this seller.