How to work error "Found on a Purchase Contract" when unchecking Inventory Item flag in Item Define?

PeopleSoft Financials and Supply Chain Management 9.2

From the Item Define page, when we uncheck the Inventory Item flag under the Item Type box several errors appear in a new tab Item Type Errors. One of them being "Found on a Purchase Contract". What do we have to do to resolve this? At the end the item needs to stay on the contract we are only removing it from being an inventory item.