Fatal error: Class 'N2PluginBase' not found
PHP error
Fatal error: Class 'N2PluginBase' not found
Other possible error: Class ‘N2CacheImage’ not found
Solution
Follow the "alternative update" documentation's FTP method:
The problem is caused by that installing/updating your Smart Slider 3 didn't worked, some of the files are missing probably because of a server issue. A reinstallation (which is the same as the alternative update) would solve the problem!