I have been to slow to purchasemy ticket online and i wanted to know if it was possible to buy a ticket at the entrence or if it's just to bad and I'd have to wait to 2012 to get to Mytodea?

You can buy a ticket on the spot, that is no problem.

best regards

Translated from the official FACTS SHEET:
It ain't a problem to come to the CoM spontainous. Just come to the Check-In and register there.
It costs 135€ - so 10² more then the actual (prepaid) Price.

So Yep, you can buy the ticket at the entrance for 135€- cash or EC-Card accepted, but i think cash is preferred. Only limitation is that you can get no NSC Tickets there, as well as there might in a rarely chance be that some camps are full, so you have to choose another. But aside of this you are free to come there and get to the big fun