[kh99]

Oh, yeah, that was asked a while back and I forgot to get back to it. Anyway, when a user requests the registration page, the mod adds the start time as a hidden value, and it also adds a check value so that the start time can't be faked. So if you get the message that it's missing or invalid it means that the check value wasn't submitted, it expired, or someone tried to fake it. My guess would be that it's either someone trying to submit a registration form without having requested the page first (like maybe some bots work that way), or else someone started a registration then left the browser window open and tried to complete it much later (like hours, but I don't remember exactly).