If you are working with network datasets that have been upgraded to the latest schema, Add the alternate ID fields before running the tool. For example,In catalog window, open the properties for the turn feature class. From the general tab, determine the max number of edges. On the fields tab, add fields with names AltID<n> of type Double for the number of edges that you have. So if you have 5 edges, add five AltID fields called AltID1, AltID2, AltID3, AltID4, AltID5 and run the tool.