There may be an issue with the current files that are loaded for the editor. You should try replacing them with the downloaded versions to see if it clears up the issue for you. Before you use the downloaded files make sure to backup your existing site and replace all of the files and folders except for the following:
You should leave these alone and replace all of the other files and folders. After you have copied over the new files you can check to ensure that they are not read only. If you still experience this problem after trying this please post back and let us know.