If you've installed version 2.6 you may notice the editor button has disappeared - this wasn't the intention.
After releasing the new code I installed it on my own live site and noticed that this was occurring - unfortunately, I'd forgotten to test the new editor button code after minimising it, and this was the cause.
I have a new version available for release but don't intend to do anything for a few days, in case any more problems are found.
If, meantime, you'd like a temporary fix to the problem you can do the following. Open up the file aye-add-mce-button.php from the plugin's includes folder. Now find the line...
$plugin_array[ 'YouTube' ] = plugins_url() . '/youtube-embed/js/aye-mce-button.min.php';
And change it to..
$plugin_array[ 'YouTube' ] = plugins_url() . '/youtube-embed/js/aye-mce-button.php';
Apologies for any inconvenience caused.