When you enable plugin, you can't add new calendar, because parameter "driver" is not passed into props attribute of button command. JS expect json there and got empty string => crash. So, I found function which add this props (calendar_ui.php, method calendar_create_menu), but this method is never called during render. If I uderstand it right, reason is that in template, you used roundcube:button, not roundcube:object. And here, I got stuck because I don't know roundcube. For a hot-fix, I filed props with json manually and it works. Maybe you know what to do...
When you enable plugin, you can't add new calendar, because parameter "driver" is not passed into props attribute of button command. JS expect json there and got empty string => crash. So, I found function which add this props (calendar_ui.php, method calendar_create_menu), but this method is never called during render. If I uderstand it right, reason is that in template, you used roundcube:button, not roundcube:object. And here, I got stuck because I don't know roundcube. For a hot-fix, I filed props with json manually and it works. Maybe you know what to do...