Actually, the warning is not about Ad Widget Lite, rather it is about the plugin Wordpress Ad Widget by Broadstreet Ads
(But I'll bet the title made you look didn't it? <grin>:wink:
This plugin overwrites the WPMUDEV Ad Widget Lite plugin folder with its own folder by the exact same folder name as the plugin folder of Ad Widget Lite.
Not a big problem, but it can be a big surprise that might not be noticed immediately.