Can't switch accounts

I used this account (d***d@tidewatercreative.net) to trial WMPU Dev and I am trying to register the website: super***.wpengine.com with a new WPMU Dev account (a**m@cbn.org) but it will not allow it even though I have removed the site from "My Sites."

I receive the following error when I try to login with the new non trial account:

"This domain has previously been registered with WPMU DEV by the user (d***d@tidewatercreative.net). To use the dashboard plugin on this domain, you can either login with the original account (and upgrade it if necessary), or upgrade your trial to a full WPMU DEV membership."