what I would do is convert the generated abstract class to a concrete class
(by removing "abstract" keyword) and then fill in the implementation.  This
is because the asp.net webservices runtime depends on attributes that are
applied to classes to modify its behavior in serialization and so on.   The
generated abstract class will have all the right attributes.  But a derived
class will not have those attributes, and the asp.net runtime doesn't
inspect the ancestors to sniff for the attributes.   So if you inherit from
the generated abstract you must also cut-n-paste the generated attributes.
At this point it is probably easier to just convert it to concrete.

Be careful about re-generating though - you could lose your changes if you
are not careful.

-Dino