I had this problems a few weeks ago, but it still gave me the game.

Maybe you're accessing the store of a different region? This could happen if you click on certain steam links here. Best solution is to remove all steam cookies, or buy directly from the steam client.

I'm pretty sure it's a restriction on the amount of games you're allowed to buy in a short period of time - to help combat fraudsters buying a huge amount of games. Just contact steam, they'll fix the problem for you. In the meantime ask a friend to buy the games for you (steam wont reply in the time frame you need).