Error 0x801901F7

Value: -2145844745 | 0x801901F7 | 2149122551

What does it mean ?

HTTP_E_STATUS_SERVICE_UNAVAIL  
Service unavailable (503).
Value: 503 | 0x01F7 | 0b0000000111110111

Where does it come from ?

FACILITY_HTTP  
HTTP support
Value: 25 | 0x019 | 0b00011001

Other Errors for FACILITY_HTTP