What are the permissions for the CMS Editor role? I would try using the security debug and it will tell you what permission is missing.
In one browser login as admin, prepare the debugging. Open a second, other browser and get ready to access the page. In the first browser, clear the debug log (so you do not have to go through lots of logs). In the second browser, perform given action as the user. Get back to the admin browser, refresh the security debug and you should see what permission is denied.
Is the user able to access admin UI or not?