About starting Schematic Dataset Editor
There are two ways to start Schematic Dataset Editor: either from the Catalog window by clicking the Edit menu 
that is displayed when you right-click a schematic dataset or by launching the SchematicSchematicDatasetEditor.exe program installed in your <Drive:>\Program Files\Desktop10.0\ArcGIS\Bin folder.
Caution:Schematic datasets based on ArcGIS Schematics versions prior to 10 can be opened using the Schematic Dataset Editor, but they open in read-only form and you cannot make changes to them. Some items, such as properties, behaviors, and environment settings, were specific to prior versions and not applicable in this version; these items are not displayed. If you need to make changes to a schematic dataset based on a Schematics version prior to 10, you must either edit it with a prior version of the software or use the Migrate to the current Schematics version command to migrate the schematic dataset and convert it into this new Schematics version.