Type constraint cannot be a 'NotInheritable' class
A constraint list includes a class that is marked as NotInheritable.
A constraint list on a type parameter can accept at most one class. A type argument supplied for that type parameter must inherit from that class. Therefore, the type parameter cannot accept a sealed, or NotInheritable, class as a constraint.
Error ID: BC32060
To correct this error
If the type parameter must be able to inherit from the class, and you have control over the definition of the class, remove the NotInheritable declaration from the class.
If the class must remain NotInheritable, you cannot use it as a constraint. Remove the class name from the constraint list.