Hi @AgaveJoe
Your approach only fixes the error in a class of BaseControlLibrary. However, my problem is calling the "Library.cs" from a Control of the "BaseControlLibrary". Now it consists of many 3 Controls Panel, Button, and CheckBox. In the future, I will add other Controls to "BaseControlLibrary". My screen capture for the "Panel.cs" shows this problem. I don't know how to fix it. Please help!