The error is given by the function PreviewObject and this function queries the property Main_Panel_Id. An object of the BasicPanel class (or one of its sub-classes such as Panel) return their object ID.

What I think you have is a modal panel object not nested within a PANEL or BASICPANEL object and then the solution would be to move the USE/INCLUDE to a place inside the PANEL/BASICPANEL object.

Since Crystal is obsolete and at least 10 years old the better solution is to look at DataFlex Reports.