PO items with 2 account assignment categories

Hello

We created a PO with 140 line items with account assignment Q (Q-project make to order).

now we want to add 150 line item in the same PO for account assignment P (P-project).when we save the PO the system is displaying the below error.

Please be noted that GL code and WBS element is same for all line items in the PO.

The GL a/c entered for Line item 150 is not relevat for this project.

Message no. MM660

We are not able to add the 150 line item with account assignment P. how to add/correct it??

Regards,

Pabbati Obulesu