Sourcing to Inventory vs Vendor

To All,

In PeopleSoft version 9.1,

An item is set up as an ‘inventory item’ at the set id level. However, this item is only defined as ‘inventory’ for 4 inventory Business Unit out of 18 Inventory Business units.  At the purchasing option level, the  inventory sourcing control ‘item not stocked at Inv Unit’ is set up as ‘Error out’. The ‘Check Inventory Avail Quantity ’ is checked. The ‘Partial Qty Can Ship’ is checked. When a requisition is sourced for this item for non-inventory BU, the requisition error's out with the error message of not having quantity in the inventory. Is there a way to set