We are unable to enable the plugin. When we attempt to do

We are unable to enable the plugin. When we attempt to do so it gives an error of "You do not have sufficient permissions to access this page."

We have...
- installed/removed the plugin multiple times
- removed old database tables and reinstalled
- added "define( 'MEMBERSHIP_MASTER_ADMIN', 'ouradminusername');" to wp-config.php
- logged out/logged back in

...and still can't enable the plugin!

I have enabled "support staff access", please investigate and fix.

Thank you!