What I'm looking for is the developer console, that should open when you hit F12, at least in Chrome. My bad though, I probably shouldn't have gone with the assumption you use Chrome, but any browser has a developer console. Here's an example with an error.
Just to be sure, the same error occurs if you try to open a file saved in a newer version of Construct. You did not happen to accidentally work in a beta release somehow? Either way, your file is not necessarily corrupted beyond repair. If you post it here via dropbox or something I can take a look at it. Often times the corruption is limited to a few eventblocks and fixing it takes 2 minutes.
As to why Construct cannot detect faulty saves... I don't know. I doubt there's no measures in place at all, just that there could be cases where it's simply not detectable?