Error 0x8004501C

Value: -2147200996 | 0x8004501C | 2147766300

What does it mean ?

SPERR_UNDEFINED_FORWARD_RULE_REF  
A rule reference in a grammar was made to a named rule that was never defined.
Value: 20508 | 0x501C | 0b0101000000011100

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

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