Error 0x8004004B

Value: -2147221429 | 0x8004004B | 2147745867

What does it mean ?

TAPI_E_CALLCENTER_INVALAGENTSTATE  
Invalid agent state
Value: 75 | 0x004B | 0b0000000001001011

Where does it come from ?

FACILITY_ITF  
COM/OLE Interface management. FACILITY_ITF is designated for user-defined error codes returned from interface methods
Value: 4 | 0x004 | 0b00000100

StackOverflow

Other Errors for FACILITY_ITF