Diagnosis
You want to create a request for quotation (RFQ) by referencing apurchase requisition. The reference item you want to adopt is alreadyused as a reference in this RFQ.
You have maintained a vendor that is defined as an 'E-Sourcing' vendorin Customizing, so that the RFQ you are working on will be sent to thelinked E-Sourcing system. However, to avoid double procurement, it isnot possible in this integration process to reference a requisition itemmore than once in one RFQ.

Procedure
If you want to send this RFQ to the linked E-Sourcing system, use apurchase requisition item reference only once. If you do not want tosend this RFQ to the E-Sourcing system, maintain another vendor.