Hi Goutham,
If you are using table key in reading internal table , then you have to pass all keys of table.
Instead of with table key try with key in read statement.
READ TABLE lt_ZSD_O140 INTO wa_lt_ZSD_O140 WITH KEY
doc_number = ls_source-doc_number
plant = ls_source-plant
ship_point = ls_source-ship_point
deliv_numb = ls_source-deliv_numb.
Thanks,
Somesh.