The geometric network was added to a data frame with a different spatial reference. At least two datasets with different spatial references were loaded into ArcMap, one containing simple feature classes and the other a geometric network. Since the editing of projected geometric networks is not supported, only the simple feature classes are listed in the target layer dropdown list.
Try one of these workarounds to edit the geometric network:
1. Load the network into the data frame first, followed by any other datasets you want to add. The spatial reference of the data frame will be set based on the first layer added to the map.
2. Set the spatial reference of the data frame to that of the geometric network.
- Select Data Frame Properties from the View dropdown list.
- Click the Coordinate System tab.
- Expand the Layers treeview under 'Select a Coordinate System' and select one of the feature classes from the network.
- Click Apply, then OK to dismiss the dialog box.
- Start another edit session. The target layer dropdown should contain all the network classes.