If you don’t mind, could you please provide a screenshot of the error you described receiving(please remember to redact personal information)? If needed, please refer to this Community FAQ for instructions on how to attach a screenshot. Alternatively, you can also drag and drop screenshots to your response if you are not given the option to add attachments.
1) Are you Syncing to Mobile/Web? AND 2) do you use the Mobile app on your smartphone or the Quicken on the Web feature?
The Sync process has been suspected of a number of weird happenings with Quicken. Could your problem be caused by Sync?
If you answer "yes" to the 1st question and "no" to the 2nd question, turn Sync off completely. You don't need it. The Sync process should only be used in conjunction with the Quicken app for Smartphones or the Quicken on the Web browser app. It cannot be used as a replacement for backing up and restoring your Quicken data file.
If you answer "yes" to both questions, try to Reset Sync so that the current cloud sync file is replaced with a fresh complete copy Do note that a full Sync process may take many minutes to complete.
How to reset Sync to Cloud
How to turn off Sync to Cloud for the current data file