- try resetting network settings - Settings - general - reset - reset network settings
- remove your Apple ID from App Store settings - settings - iTunes & App Stores
- if the problem still persists, try:
- settings - general - date and time - set automatically - off
- set the date to 1 year ahead
- go back to the App Store and try to download or update anything, it won't work
- kill the app store, turn on Set Automatically in settings, and try downloading