Weird Windows Designer Loading Exception

Question

My designer is failing to load my form because of some weird issue.

I have a BaseForm, from which all forms are inherited. This base form also implements an interface, ViewInterface (I am implementing MVP pattern).

Now if ChildForm inherits the BaseForm, the designer fails to load ChildForm. It gives the error 'failed to load type NameSpace.ViewInterface from assembly version=x.x.x.x'

If ChildForm directly implement the ViewInterface then it works all fine.

Any ideas why ?

Note: Only the designer doesn't loads, the solutions compiles/runs perfectly fine.