Embedded Master Module. EMX and Embedded Master are essentially identical in features and dimensions.
In GHI NETMF v4.1 SDK /Embedded Master more information ( EMX vs. Embedded Master Module) , pdf file.
The document “EM vs. EMX” highlights the few differences between the modules.
(This is my interpretation of how things worked)
There used to be code that sensed the difference between EM and EMX in the firmware, that meant 4.1 could cater for both devices. That code was not included in 4.2 so you can’t use it.