I could post the last working version, but I guess that won't help much.
For me this bug seems to happen if I run Construct a quite long time, change lots of things in my project and keep saving. Sooner or later that'll break my file. When I try to reopen it later on, it'll give me that error message.
So now I'm doing what deadeye mentioned in another thread: I'm working a little bit with Construct, then I'm saving and RESTARTING it. And I restart it often. Haven't encountered the bug since I use to do so.