We have had some instances where our emails go to users junk/spam folders. Please check if there is an activation email from us in there.
Our account activation links time out after 1 hour. If you click through the activation link when the link has timed out you will land on a page that says "Invalid Signature". If this happens to you, you can send yourself a new link by going back to the login page and clicking the "Activation Link" text.
Then enter your registered email address.
If you continue to have any trouble please submit a request, or contact firstname.lastname@example.org.