 <p>The problem is not that the class is a <code>partial</code> class. The problem is that you try to derive a <code>static</code> class from another one. There is no point in deriving a <code>static</code> class because you could not make use Polymorphism and other reasons for inheritance. </p> <p>If you want to define a <code>partial</code> class, create the class with the same name and access modifier. </p>