GR Problem

hi all

good morning,

can we do the GR for excisable items against one invoice ?

i have one cenvat item "A" with qty 100in PO 1001. first tim i made gr for this item with qty 30 against invoice : 123 & PO 1001 , but next time for the same PO 1001and same material with remianing qty 70 when i go for MIGO against invoice : 123, system shows GR already done with this invoice.

i need to remove this error because it is not possible that vendor can give total qty at a time.

can anybody suggest me ?