I have a SAMSUNG SGH-T589. I have put my google account and the gmail is synchronizing well and the default app store (Market) has updated to Google Play Store v 3.9.16 but when I try to download any app from it, I get an 'Authentication is required. You need to sign into your Google Account' error. I don't, however, get any option to sign in again. I cannot remove the account without resetting the phone which I tried with the same results. I have also tried to clear cache and data for the Google Play App, restart the phone several times with the same results. Nothing seems to be working. Can anyone suggest anything I can do?