BuddyPress.org

Set your current new user to be the Site admin user.

You will need access to the database, look in wp_sitemeta for a line with a meta_key of site_admins. It will currently look like:

a:1:{i:0;s:5:”admin”;}

You need to change the admin to be your new users name, and the s:5 to be the length of your new user. E.G.

a:1:{i:0;s:9:”spacetest”;}

spacetest is nine characters long so I’ve changed s:5 – s:9

When you next login your new user will be the site admin user, and you can access the plugins menu.

From wordpress MU post:

https://mu.wordpress.org/forums/topic/13444?replies=8#post-78799