Impossible to buy Minecoins

When i try to buy Minecoins on the Marketplace a window open that say "An error has occured. Unable to connect to the market. Maybe you should check your Internet connection." (approximativly, it's translated from french, i don't know what is exaclty told in english)

I tried for weeks, i've search a lot on the internet but i've found no one with the same problem.

Please help me.