Error 0x80310020

Value: -2144272352 | 0x80310020 | 2150694944

What does it mean ?

FVE_E_OS_NOT_PROTECTED  
The operating system drive is not protected by BitLocker Drive Encryption.
Value: 32 | 0x0020 | 0b0000000000100000

Where does it come from ?

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

Other Errors for FACILITY_FVE