Fatal error with Avatars plugin

Just installed the Avatars plugin and got this fatal error message:

Fatal error: Class 'WA_Widget_Avatars' not found in /home/healthli/public_html/wp-includes/widgets.php on line 413

I try to go to network admin>plugins to deactivate the plugin or some others to see if there's a conflict, but just get a page with the error.

But if I edit a user on a subsite, the option to change the avatar is there. It let me upload an image, but then shows a broken image icon.