We just encountered this error today when trying to export from QuickBooks Payroll to Quickbooks Online. It looks like none of the suggestions here are correct. Here is the solution that we found that worked for us:

1. Ignore the suggestion to login to Quickbooks Online

2. Stay logged into Quickbooks Payroll and go to Settings (gear) > Payroll settings > Export > Edit (pencil)

3. Next to where it says "Quickbooks Online (company name)" click on "Change"

4. This takes you to Export Preferences. "Quickbooks online" should already be selected. Click "Save".

5. You'll now be prompted to login to your Quickbooks Online account from *inside* Quickbooks Payroll, which will re-establish the connection from QB Payroll to QB Online.

Wow... sure would be nice if this information was available from QuickBooks. Hope this helps someone else!