This blog is based on a true story from a forum post. Hopefully it will help others that have the same issue.
Problem: I have created a mosaic dataset and added a raster in it. Then I opened the attributes table and clicked on Start Editing in Editor toolbox. It is giving me the error that there are “No editable layers”.
Is your Mosaic Dataset stored in SDE?
Solution: If so, you will have to register the footprint layer as versioned. Add the mosaic dataset is added to ArcMap, you can run the Register As Versioned geoprocessing tool and select the ‘Footprint’ layer.