Activation Link does not work

I’ve got a WordPress 3.0 installation over at https://tabletopgeeks.com/

Users can register and sign up for a username and a blog. If they choose to sign up for both they receive an email with an activation link. Clicking on the link doesn’t work though. The activation link looks like:

https://test3.tabletopgeeks.com/wp-activate.php?key=b78310b66a786876

When you click it, it redirects to:

https://test3.tabletopgeeks.com/wp-activate.php?action=lostpassword&error=invalidkey

And prompts for the activation key. If they copy/paste the activation key from the url and enter it in this box, activation works fine. Why won’t the link work, though? I’ve been searching for hours and I can’t seem to find anything on this.