Follow the steps:

1.Create an application and add a RadRibbonForm with name RadRibbonForm1.

2. Create a new class with name RadRibbonForm1.Test.cs and make it partial. It should look like a form.

3. Double click the new class. It will open the designer and some code will be generated in the class which prevents the application from building. The attached gif file with RadRibbonForm illustrates better the specific steps.