Hi william,
This issue can occur if you activate your account multiple time with the same key, for instance by open the link provided in the automatic BuddyPress email in your browser and then, by manually entering the key in the activation form. This can be also happen when you try to use different sessions (administrator and test subscriber) with the same browser and follow the activation link several times in a row.
This issue can also occur when your activation email is either not send by your server -for instance, when mailing services are incorrectly set- or not received by your registering user because of his mail client spam filter.
Unfortunately, this issue is related with BuddyPress and the installation, setting or debugging of third party plugins isn’t part of the support we will provide for our theme (Gwangi) and our plugins (Grimlock suite).
We suggest you to ask for more help on the BuddyPress support forums:
https://buddypress.org/support/
You might also be interested by the following BuddyPress support forum topics about this issue:
https://buddypress.org/support/topic/new-user-registration-problem-invalid-activation-key/
https://buddypress.org/support/topic/need-activation-key/
Regards,