Class '<classname>' must either be declared 'MustInherit' or override the following inherited 'MustOverride' member(s): <membername(s)>
Classes derived from base classes that contain MustOverride members must either override such members or use the MustInherit modifier.
Error ID: BC30610
To correct this error
Add the MustInherit modifier to the class definition.
Declare an override using the Overrides keyword.