When we have multiple projects in workspace, we have to set the references between the projects, not among the projects. If P1 references P2, P2 references P3, and P3 reference back to P1. That will cause a cycle.
The Solution is to draw a Diagram of the reference between projects in workspace. Check the Java Build Path of each of the projects to see the Tab of the Projects window. Take out the Project that are refering back to the main project, e.g. P3 references P1, in this example above.
Detailed operation is to select P3 project in RAD OR eclipse, right click on the project and choose the properties option, it brings up a new window for properties of P3. Click on the "Java Build Path" section, Choose the "Projects" option Tab. You can see the P3 has referenced P1 in the field. Select the P1 reference, click "Remove" button on the right side of the window. Then, click okay. The IDE will start to reset the path automatically.
Done.
Keep find all of the mis-referenced reference in every each projects until you have the right references to each of the projects in your Diagram. Good Luck!