Relation between EOAWTHREAD_ID and EOAWPARENT_THREAD

Hello Experts,

Our users are getting a fatal sql error when they select a voucher work list item. It's only happening randomly(only for certain items).

The system log shows that a sub query is returning multiple rows for an update statement.

Here is the snapshot of the error.

Error Position:  48

  Return:  1427 - ORA-01427: single-row subquery returns more than one row

  Statement:  update ps_eoaw_summ_dtl set eoawustep_status = (SELECT USTEP.EOAWSTEP_STATUS FROM PS_EOAW_STEP_VW USTEP WHERE USTEP.EOAWUSTEP_INST_ID = (SELECT MAX(U.EOAWUSTEP_INST_ID) FROM PS_EOAW_STEPINST S, PS_EOAW_USERINST U WHERE S.EOAWSTEP_INSTANCE = U.EOAWSTEP_INSTANCE AND S.EOAWPRCS_ID = :1 AND S.EOAWTHREAD_ID = PS_EOAW_SUMM_DTL.EOAWTHREAD_ID AND U.OPRID = PS_EOAW_SUMM_DTL.EOAWAPPROVER_OPRID AND S.EOAWSTEP_STATUS <> 'B')) WHERE PS_EOAW_SUMM_DTL.EOAWPRCS_ID = :2 AND  PS_EOAW_SUMM_DTL.EOAWTHREAD_ID IN (26612) AND PS_EOAW_SUMM_DTL.EOAWAPPROVER_OPRID IN (SELECT USTEP.OPRID FROM PS_EOAW_STEP_VW USTEP WHERE USTEP.EOAWUSTEP_INST_ID = (SELECT MAX(U.EOAWUSTEP_INST_ID) FROM PS_EOAW_STEPINST S, PS_EOAW_USERINST U WHERE S.EOAWSTEP_INSTANCE = U.EOAWSTEP_INSTANCE AND S.EOAWPRCS_ID =