Does the problem still occur with the latest version of ImgBurn? The latest version has a lot of changes and fixes.
Do you get the same error when you do a test burn (simulation)?
Also, do you use the setting "when saving leave at least 32k between ifo and bup"?
Do you use the seamless layerbreak option when selecting the layerbrake just before burning?
I've only had one error with ImgBurn. I couldn't burn a certain .ISO but I got the error before the actual burning started so I didn't loose any discs. Eventually I gave up. It must be so frustrating burning a discs and having an error pop up during finalizing. It would drive me nuts too.
If nothing else works I would buy a new burner I guess.