Can't download free apps from App Store since I downloaded IOS 7. Any ideas?

I can't download free apps from the App Store after I downloaded the IOS7. I've tried reloading settings, but still can't. Soon after downloading the new system I had to redo my apple username and password. Soon after that I tried downloading, and I couldn't. It says "this app cannot be downloaded at this time, try again later. Last night I successfully downloaded a paid app, but that just made me madder. What's up?