R12.2 adop phase=prepare Failed While Synchronizing Snapshots

Error: remote_execution_result_20150619_122924.xml file shows following error.
Synchronizing Snapshots...
  [ERROR] Failed to execute SQL statement :
  begin
  ad_zd_adop.sync_snapshots(342);
 exception
  when others then
  update ad_adop_sessions set status='F'
  where adop_session_id=8;
  commit;
  raise_application_error(-20001,'Error while calling ad_zd_adop.sync_snapshots.' || sqlerrm);
 end;
Sol:
1. Execute the following script from SQL command prompt:
begin
   ad_zd_adop.sync_snapshots(342);
 exception when others then
  raise_application_error(-20001,'Error while calling ad_zd_adop.sync_snapshots.' || sqlerrm);
 end;
end;
/
2.  rerun adop phase=prepare.