Have you tried deleting the CPD file before opening the project?
You seem to know which topic it is. Move it outside the project and then open the project. Maybe then importing it will clean things up.
Do you have any backups?
Try it this way. From RoboHelp, right-click the topic in the Project Explorer pod.
Choose Explore and Windows File Explorer should open
Now locate the topic in Windows explorer. Right-click it and open it in either notepad or your browser.
Select all the content and copy to the clipboard.
Go back to RoboHelp and delete the topic.
Create a new topic to replace it with.
Paste the content into the editor and remove unwanted bits.
Let us know how well that does or doesn't seem to work.
Thank you, gentlemen!
Rick, I tried your suggestion, but when I opened the file, I got a page full of gobbledygook and gibberish (you would probably call it "code").
I deleted the CPD file, Peter, but I think that partially deleted my topic; fortunately, I did have a backup in a zip file, so I created a new topic in RH, then copied-and-pasted the "old" topic into the new one. I still don't know what the problem was, but I suspect it had to do with the image in the topic, as I had selected it and was about to replace it.
Anyway, better now.