Error 0x8031001D

Value: -2144272355 | 0x8031001D | 2150694941

What does it mean ?

FVE_E_KEY_REQUIRED  
One or more BitLocker key protectors are required. You cannot delete the last key on this drive.
Value: 29 | 0x001D | 0b0000000000011101

Where does it come from ?

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

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