sorted  duplicates  are  only  valid  within  a   nested   index
  definition

  Explanation:  If the duplicates handling is specified as sorted,
  then a nested index definition must exist.

  User Action:  The index can  not  be  created  in  this  manner.
  Recreate  the  index without the duplicates are sorted clause or
  with a nested duplicates index, specifying that  the  duplicates
  are to be sorted.