Thanks for letting us know. I'm fairly certain that the JS is okay, as this is the first time the issue has been brought up, but we will throw that error in the event that someone has already signed up for Meeet's mailing list. Could have you put in your email prior to that?
Yeah - I'm fairly certain that's exactly what the issue is. The reason you're not seeing the real error is that we get the errors via not-so-readable JSON from the Mailchimp servers, and the JS email library we are using displays that error message for ANY error returned by the server to keep things simple and prevent confusion, though it seems to have caused a bit of confusion here.
There's a chance we may change that in the near future. Again, if you want a sticker, feel free to drop us a line on Twitter, we'll follow you, and you can DM us your address. We have plenty! :D