Error 0x80310009

Value: -2144272375 | 0x80310009 | 2150694921

What does it mean ?

FVE_E_ACTION_NOT_ALLOWED  
BitLocker Drive Encryption cannot perform the requested action. This condition may occur when two requests are issued at the same time. Wait a few moments and then try the action again.
Value: 9 | 0x0009 | 0b0000000000001001

Where does it come from ?

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

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