Multi-Site Unit 5 - Issue with activating a new site

Hi All,
When I click on the activation url to create a new site on my multi-site network - I get this error msg:

Not Found

The requested URL /wp-activate.php was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I am also getting errors after creating new sites in my multi-site network. When I click on "view" to view my new site, I get the index page (see here: