When the extension encounters an error, it logs it in a separate error log file in Magento. This file can be found under var/log/nostotagging.log. Only errors the extension can recover from are logged here, and PHP fatal errors, for example, are logged in the default Magento error logs located in the same directory. This is because these kind of errors stop the execution of the code and Magento's error handler takes over. Fatal errors are only thrown by critical bugs in the extension, which are very rare.