I was playing around trying to design a button and I came up with using a Border with a Button on it. Then I changed my MyClass to derive from Border. Border is a sealed class so the compiler flagged an error. So I removed the ": Border" from the class definition. Now however I still get a
Error CS0509 'NumberedButton': cannot derive from sealed type 'Border'
As it's a partial class I wondered where else in the bowels of the project there is a memory of this? I've searched all the textfiles (I think) and come up empty-handed. See the snip on Imgur