error when activating avatar plugin

When I activate the Avatars plugin (v3.5.4) on my WP 3.0.4 multisite I get the following error:

Fatal error: Allowed memory size of 20971520 bytes exhausted (tried to allocate 311296 bytes) in /usr/www/users/xxxxx/wp-admin/menu.php on line 235

I have installed other wpmudev plugins and this is the first error I am getting. I had to delete the avatars folder in order to access "plugins" again in the admin section.