@dragongfx,
I am experiencing the same issue. Also being told I didn't check the agreement box when I clearly did.
Out of curiosity, how are you trying to order? Using PayPal or a CC? And if the latter, do you have a CC with one of the 6 European banks listed?
I ask because I was trying to order using a CC, but as I live in the USA, my CC is obviously NOT issued by AMRO or any of the others they listed. I didn't know if the page was blowing up on me because of this or not. But the part about the agreement apparently is affecting others, as indicated in this other thread titled "Trouble with pre order":
http://80.95.161.114/shipsim/forum/index.php/topic,19836.0.html
So you're not alone.
@Kristian01
Not familiar with GamersGate. How is it that you believe you can get access to pre-order extra content using that?
I Googled and eventually found this page:
http://www.gamersgate.com/DD-SSE/ship-simulator-extremes
But it does not say you'll get the extra vessel and missions. It talks about "blue coins" and things which I think are only relevant to the gamersgate.com website.