Hello Stefano,
Today I installed your plugin on my site. Everything works just fine, except for the visual editor while creating newsletters. I noticed that some parts of the subscriber tab weren’t working, so I presume it’s a JS/CSS problem. I tried deactivating some other plugins, and I found out that the Events Manager plugin (http://wp-events-plugin.com/) caused some trouble when it’s activated. Without this plugin, everything works fine. Is this a known issue?
Thanks in advance!