NullReferenceException when doing InsertOnSubmit in LINQ to SQL

Question

In my database I have a table called StaffMembers

when I bring this into my .net Project as through linq-to-sql an entity class StaffMember is created

Now I have

Answer 1

Sometime, just forgot to add this line to the base class:

[InheritanceMapping(Code = "Class", Type = typeof(Class))]