iPhone 4 - Verification Required

I've been using the App Store through my Apple ID for a while and everything has been normal.

Now, all of the sudden, when I want to update an app or to download a free app after putting my password a pop-up message appears entitled:

Verification Required

asking me to verify my payment info. In my phone's account settings, the payment information is set to NONE since ever, still there's a red message up saying:

You must verify your payment info before you make purchases.

The thing is, I don't have any payment info, that is why I only use free apps. What to do?

Select Verify Payment Info, and under Credit Card, just choose None. If this doesn't work, close the App Store and go to Settings > App Store > Tap on your Email > View Apple ID > Payment Information > None.

This should fix the issue.