To my knowledge, CC does not tell you where the problem is. That might not be a simple question to answer. I don't know the filling algorithm used by any of these programs, but I suspect it's pretty much brute force. CC uses a fair amount of processor power when it's working. At some point, it gives up. Seems to work on a section of the puzzle at a time. Maybe it could say what quadrant it was on when it quit, but you can tell that just by watching it (assuming it at least tries to fill for awhile, which I know it doesn't always do). Anyway, as a general matter, while there may be a word or two that could be changed and thereby make the grid fillable, I don't think the software has any idea which ones they would be. Seems like the theme answers are usually the killers. Try backing them out one at a time, maybe?
That's not much help, sorry, and I should point out that I'm very new at this.
Alas, I don't think there is a version of CC that runs on Macs.