Data for this user has not been imported. This user does not exist in AD, is improperly homed or has not yet been synchronized ...

Data for this user has not been imported. This user does not exist in AD, is
  improperly homed or has not yet been synchronized by UR. If the user still
  exists in AD, retry the import for this user after synchronization is
  complete. If the invitee no longer exists in AD, you may ignore this error.