Couldn't sign in error message on gmail app

I have a Galaxy GS3 phone. In the last day or so I have been getting a "couldn't sign in" message for primary emails on the gmail app. There is a sign in box to the right, but it just puts me back to that error message when I use it. There are no other error messages. For example, I can't tap on the error message and see any additional explanation. Interestingly, I can look at other folders such as the Sent folder and read those emails (although they don't appear to be updated recently), but I can't access Primary, Social, and Promotions without solving the sign in error.

I cleared the phone's cache by going through the battery removal and key dance and reboot procedure. That didn't help.

Any ideas on how to fix this?

I have one other google app on my phone, docs, and that is working correctly. The gmail account on my home computer is working correctly.

— modified on Apr 27, 2017, 7:56:41 PM