Action 'Merge Shipments' Error

Dear All,

I am trying to Merge 2 shipments using Merge Shipments Action. But it is throwing me an error :

java.sql.SQLException: ORA-01427: single-row subquery returns more than one row
Error creating SHIP_COMMIT_ALLOC_JOIN for shipmentGid:

Is anybody aware about this error?

Thanks..
Shital