Error 0x80310012

Value: -2144272366 | 0x80310012 | 2150694930

What does it mean ?

FVE_E_SYSTEM_VOLUME  
The drive cannot be encrypted because it contains system boot information. Create a separate partition for use as the system drive that contains the boot information and a second partition for use as the operating system drive and then encrypt the operating system drive.
Value: 18 | 0x0012 | 0b0000000000010010

Where does it come from ?

FACILITY_FVE  
Full volume encryption
Value: 49 | 0x031 | 0b00110001

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