Coca-Cola's Twitter-based Super Bowl campaign hit a snag when the drinks giant was barred from posting messages for two hours during prime time. Coke posted tweets thanking individual users for voting in an online game linked to its TV spot, but quickly exceeded Twitter's maximum-post threshold -- it had petitioned for a higher limit and even exceeded that -- and was frozen out of the service. The episode highlighted the difficulties brands can face when running major social campaigns, writes Cotton Delo.