app store error message "could not sign in" "an unknown error has occurred"

I experienced this problem, too -- and with the help of an Apple support rep, figured out a way out.

Go into Settings and turn off automatic date and time, and set your phone back a year. Then go back and turn automating date and time back on, to get back to the present. Now go to Settings > iTunes & App Stores, click on your AppleID, and re-enter it and your password. Finally, go back to the App Store (or iTunes Store) and try to download what you had been trying before -- and if you're like me, it will now pop up with a new set of Terms and Conditions for you to approve. After you approve, you'll be able to download whatever you had been trying to.

It appeared, in my case, that Apple needed to present me with a new Terms & Conditions to approve, but for some reason, iOS 6 and the Apple mother ship weren't communicating correctly about how to do that, and I was stuck with the "Could Not Sign In" message. Changing the iPhone's time and/or re-signing in via Settings > iTunes & App Stores resolved the roadblock for some reason. Hope this works for others as well!

Thank you so much! This trick worked for my son's new iPod. I didn't have to review any new terms and conditions, but setting the date back a year and then resetting it to automatic did the trick. Thank you, thank you, thank you!!!

Worked for me too, many thanks

This worked for me. Thanks a lot.

Worked for me too, thanks 🙂

sadly , not woking for me ...if I go though those steps it just want a new account ... complete with new password ... no mentio of my gift card preloaded.

Awesome, Eric!

Worked like a charm.

Thanks!!

Bogus solution - Like fake news. I have been working on this for 90 minutes. I cannot sign-in to my Apple ID with my iPhone. PC is fine. This was only a minor annoyance until I can no longer use my online bank, because I cannot update my Apps, because Apple says my ID and password combination are incorrect. This comes after discovering Apple is placing ads on my calendar!!! Also after ITunes not longer converts my music to mp3. Also after My iPhone is not recognized by my computer, so there's no way to download the pictures I take with the phone. Are you trying to make things better or worse over there?