Hi Pavan,
In function CRM_ORDER_READ_OW, which is called inside CRM_ORDER_READ, the related item is inserted into the table et_orderadm_i more than once and the runtime error is raised: ITAB_DUPLICATE_KEY.
This might be because of the duplicates being passed through it_header_guid.
Please provide your Exit to see what we can help.
Br, Andras