Item &1 is assigned with both F and C ARun status; Refer the Long Text.

What causes this issue?

Document item is relevant for Supply Assignment (ARun).
Document item has assignments in both Ready for Delivery (F) and IFO
Assignment (C) ARun status; Outbound delivery can be created for the
quantities in Ready for Delivery(F) ARun status only.
IFO Assignment quantity will be considered for delivery creation after
Ready to Delivery quantity is fully consumed.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Create Outbound delivery for the same document item to deliver the
remaining quantities with IFO Assignment (C) ARun Status.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.