I've had this same problem one day when I was downloading a lot of apps from the android market,this problem isn't coming from the phone but it is with the new android market.To fix this problem,go to settings,then applications,and manage apps.Scroll down till you find market,make sure the android market is the one you choose.From their you'll tap the market and tap the uninstall updates.After that,go back to home and choose android market,then download your app once you agree to the markets terms.