fatal error message

I got this error message on a test site that only has WPMU DEV stuff (MultiSite located at test.example.com/3/ - I know, not the way things should be, just saying):

Fatal error: Call to undefined function upgrades_show_ads() in /home/.../public_html/test/3/wp-content/plugins/upgrades-advertising/upgrades-advertising.php on line 124

I deleted plugin folder via FTP and site worked again.
Just FYI.