Hi,

We are getting the same problems very often, even without inheriting from DiagramView 8) They happen after an assembly that defines a control loaded in the VS designer is updated. Then VS might end up with two versions of the assembly loaded...

A new diagram is added automatically when the DiagramView cannot find a Diagram instance on the form. In that case there is a diagram from a different version of the assembly, the view does not recognize it and adds its own. The crash happens when VS tries to assign an object from one version of the assembly to a property of that type on the diagram or diagramview from the other version, e.g. during form initialization.

Unfortunately we haven't found any way to stop these issues, apart from closing the form and restarting VS. The next time you open the form, VS loads only the new assembly and it should work fine.

Stoyan