linking Subreport to main Report in Crystal

Hi,
I have a report listing Planned Courses.
In that report there is a Subreport that's supposed to show all the courses that took place based on the planning (one to many).

All the data comes from the same table and the 1-N relationship is achieved by a "PlannedCourseID" field that points to another record in the same table.

The main report displays all the planned courses no problem.
I tried to link the subreport to the main report on the PlannedCourseID - subreport = get all the courses who's CourseID = main report's course's PlannedCourseID but the subreport comes back empty.

I've read the documantation and tried playing with the link but nothing seems to work.

Any help would be highly appreciated!
thanx