Plugin menu not displaying for new blog administrator

Hi

My problem

The plugins menu does not display for a new blog administrator.

What I've done

Installed a few plugins on the main blog via FTP following the instructions.
Enabled the Plugins menu in Site Admin/Options
Added a new user as a subscriber to the main blog
Added a new blog with the new user as administrator

If I visit the new blog backend as the site administrator the plugins menu displays as expected. Logged in with the new blog administrators username and password the plugins menu doesn't display.

Any help would be greatly appreciated.