The directory "advanced-iframe-custom" could not be created in the plugin folder. Custom files are stored in this directory because Wordpress does delete the normal plugin folder during an update. Please create the folder manually.
The file "advanced-iframe/js/ai_external.js" can not be saved. Please check the permissions of the js folder and save the settings again. This file is needed for the external workaround! If you don't use the external workaround please create a empty file with the name ai_external.js in the js folder of the plugin.