Can't log in on AppStore and iTunes on my iPad Air 2

I Have an iPad Air 2 with iOS 8.3, I found an app to download, I pressed "GET+" and it doesen't download, unless I've already logged in on AppStore/iTunes, then I went to Settings -> AppStore and then I logged off my Apple ID, then I see I can't log in, so I checked my Apple ID and password if I made any spelling mistakes, but it was correct. I think Apple must fix some bugs on AppStore and iTunes in nex update as soon as possible... Any Ideas?