Hi Rico,
There should be two files associated with the Form, one with formname.cbl and one with formname.Designer.cbl. Both need to be present when you add them to the project.
If you double-click on the formname.cbl and it only shows the source code then you need to open it in design view.
Right-click on its name in solution explorer and select View Designer to open up the GUI representation.
Thanks.