Can you please post the source of the program that you are trying to compile?
If you are using the REPOSITORY directive with CHECKING ON then you should also have this set to use REPOSITORY with UPDATE ON in the class that you are referencing.
The UPDATE ON is what adds the class to the repository so that it can then be referenced by other programs or classes.
$SET REPOSITORY "UPDATE ON CHECKING ON"
BTW, none of this is required when using the OO syntax supported in managed code as the repository has been made obsolete by the addition of the TYPE keyword.
Thanks.