F2063 Could not compile used unit '%s' (Object Pascal)
This fatal error is given when a unit used by another could not be compiled. In this case, the compiler gives up compilation of the dependent unit because it is likely very many errors will be encountered as a consequence.
The cause for the fatal error lies in the previous errors reported by the compiler, that is, the actual errors that occurred in the unit being used.
The Object Pascal compiler does not give up after the first error it finds. It tries to find all the errors in the source and report each one, so that you can fix all the errors before attempting to compile again.
However, if a unit or program uses another unit, and that other unit cannot be compiled owing to a compiler error (such as a syntax error), it is not reasonable to continue trying to compile the unit or program. There would be too many false positives; identifiers would be registered as not found, when in fact they would be found if the used unit had compiled correctly.