This is actually a recent bug several Meta Box AIO users have noticed and reported here, after the update to 3.2.0, and we were told it would be fixed in the upcoming update, God willing.
But in the meantime, what worked for me was just entering any value when requested to fill out a field. Afterwards, I am allowed to click "Save". The actual value entered is not saved anywhere that I can see, but it fulfills the "requirement" and lets me save the changes I made in the admin area.
So you can try this too if you like, until the next update comes: Just enter any value, and save. It will see the required field as filled, and should then let you save, and you should not find the value you entered saved in the database (I did not).