This happened to me either the apps are to new for your version of iOS or your app is to new if your version is to old plug it into your computer to update it. If you have a lot of updates and you have a reletivally new software update your apps. If you have a iPhone 3G or iPhone 2G or
iPod touch1st gen or iPod touch 2nd gen do update your apps because you cant update your software past iOS 4.2.1 on iPhone 3G and iPod touch 2nd gen and 3.2.1 on iPhone 2G and iPod touch 2nd gen