After I changed a setting in the ckeditor plugin, the content of the whole manager doesn't load. Only the menus (top and left) are shown. I've already cleared the cache by deleting the content of the core/cache folder, and the cache from my browser.
Remove the core/components/ckeditor folder and clear cache again. Login in the manager, go to packages Manager and remove the ckeditor and reinstall. This is also a way to remove manually packages in modx.