Error 0x800721C8

Value: -2147016248 | 0x800721C8 | 2147951048

What does it mean ?

ERROR_DS_UPN_VALUE_NOT_UNIQUE_IN_FOREST  
The operation failed because UPN value provided for addition/modification is not unique forest-wide.
Value: 8648 | 0x21C8 | 0b0010000111001000

Where does it come from ?

FACILITY_WIN32  
Provides a way to handle error codes from functions in the Win32 API as an HRESULT. (Error codes in 16 - bit OLE that duplicated Win32 error codes have also been changed to FACILITY_WIN32)
Value: 7 | 0x007 | 0b00000111

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