I think I would be very patient (while chewing my nails) and wait a day or two more hoping that someone who knew what CNO means would tell me what to do.
Your messages indicate you can open that project. What are or were you doing when the CNO warning popped up? And what did you do then? and what happened? What other programs were also open at the time?
As long as you can open the project, try this. Open the program and project. On the toolbar across the top of the project, click Utilities, Project, Check.
I want you to have only the following boxes checked. Everything else should be empty. In the Project list only, add a check to everything in this group EXCEPT Add Birth/Death . . .., GEDCOM . . ., and Streamline . . . Those three boxes I want blank.
Click on Repair. This will probably not take long. When the program has finished and repaired, you can see (posibly hiding behind another window), the list of what was repaired. Don't worry about what it says. Just escape.
Go back and click Utility on the Toolbar, then click on Reindex. Click OK.
Close UFTree. Shut down the computer. Power up, and try again. If your CNO doesn't show up again, no problem. Tell us yes it is fixed or no, still a problem.
I hope you have made a backup of that project. I hope you have backups of the other projects.
By the way, if this happened while you were importing into TMG, be aware, UFTree should be closed when you are importing into TMG. And don't use GEDCOM. Use GenBridge.