Diagnosis
You are trying to select HUs which do not have a reference and thencreate a referencefor these HUs for the selected document (request, order, delivery).

Procedure
Select just one header row. For the material for this request item,order item or delivery item, HUs without areference are selected. In thefollowing list display you can then select for which HUs you want tocreate a reference. To do this, chooseCopy or Transfer HUs. The corresponding reference is thencreated for these HUs.