Notice: Undefined variable: ret in …/class/Output.class.php

Notice: Undefined variable: ret in /var/www/wp-content/plugins/simple-google-analytics/class/Output.class.php on line 139

Simples solution would probably be to change this:

// Ecriture des options
			$ret .= '<script type="text/javascript">' . "\n" ;

to this:

// Ecriture des options
			$ret = '<script type="text/javascript">' . "\n" ;

https://www.ads-software.com/plugins/simple-google-analytics/