Did you run Apply Asset Package against the utility network in Communication_UtilityNetwork.gdb that is shipped with the solution? If so, there is no need, that GDB was created via the Asset Package to Geodatabase tool prior to packaging. It is a fully built utility network.
If you want to create a new GDB and Utility Network with the data you added, then use the Asset Package to Geodatabase tool. I would suggest reviewing the task highlighted below. They will walk you through the process to set this up without the sample naperville data.