W1004 Unit '%s' is specific to a library (Delphi)
Go Up to Error and Warning Messages (Delphi)
The whole unit is tagged (using the library hint directive) as one that may not be available in all libraries. If you are likely to use different libraries, it may cause a problem.
The $WARN UNIT_LIBRARY ON/OFF compiler directive turns on or off all warnings in units where the library directive is specified.