RESERVE can not be used with ADD/DROP in the same ALTER DATABASE
  command

  Explanation:  RESERVE STORAGE AREAS  cannot  be  specified  with
  either  ADD  STORAGE AREA or DROP STORAGE AREA in a single ALTER
  DATABASE command.

  User Action:   Perform  RESERVE  STORAGE  AREAS  in  a  separate
  command from either ADD STORAGE AREA or DROP STORAGE AREA.