Hi Richard, I have had this issue as well. The layer control within the schedule environment is a bit of a joke. Try this:
1. exit the schedule
2. turn on relevant / all layers
3. Open the schedule via Document>Schedules>Scheme settings
4. Hopefully now the elements will be selectable and editable.
4. Lastly, delete your old view in Viewmap that linked to your schedule and create a new one with the new layer settings
There seems to be a bug with schedules that means the layer combination is only ever set wehn you first create the view and updating a layer combination doesn't seem to help.