Thank you for
reaching out on the community and telling us about your issue. If you go across the top to window -> account status do any of the Financial Institutions listed give the error message? Have any of your FI's changed your account numbers in recent memory as well? Check the registers as well to see if there's an account that hasn't received any data for the time period the error has been popping up. Once we're able to find out which FI is causing it we're able to try troubleshooting it.
Start with saving a backup in quicken. In the top left go to file -> save a backup and choosing where you'd like to save it. Once that's done we should need to deactivate and reactivate the account. If you're still unsure which account it is, deactivate all of the accounts with the FI and reactivate them right after.
Here are articles in regard on how to deactivate and reactivate the accounts.
Please let us know
if this helps resolve the issue for you.