Membership - Network Activate - "You do not have sufficient permissions to access this page.&qu

Hi,

I'm trying to Network Activate the Membership plugin, however when I do so I get the error "You do not have sufficient permissions to access this page."

I am using a username other than 'admin' as I am hosted on WP Engine. The usage page for the plugin states:

For security, the membership plugin is set up to provide it’s membership options to the admin who activates the plugin. For many reasons, you may be using an account other than ‘admin’ this can be changed with a simple constants, please review our 60+ page manual for further information.

This is okay - but I can't find the manual for the Membership plugin, either on the plugin's page or in the zip. I wondered if someone could point me in the right direction - either to the documentation, or provide the information about the constants for me please?

Thanks in advance!

Iain.