It means you need to create the Topology or Geometric Network beforehand, and than register as versioned. You can't create a Geometric Network or Topology based on Feature Classes already registered as versioned.If the datasets are already versioned, you need to unregister them, create the Geometric Network, and than register as versioned again. You can than continue using the newly versioned datasets as part of the Geometric Network. Be sure to reconcile, post & compress the Feature Classes before unregistering as versioned, so as not to loose any changes.