Hi Thilini,
Please check in SM50 if any process is running from long time. Sometimes the processes get hung up and lock the transactions. In this case basis will have to kill the PID and then you should be able to run the setup table for this order.
Also if nothing works try filling up setup table only for this order and put a breakpoint (/h) while running i.e. debugging. Take help from ABAP developer.
You should be able to find out the lock for this order.
Thanks
Amit