Sorry for the trouble everyone. However, please read How to report bugs and always follow the guidelines - the original post ("C2 wont run my projects") is not a useful bug report, the first thing I did was export the Physics demo and it worked fine. I believe the real issue is this one where if you don't have a jump-thru object in the layout the Platform movement hangs, which is to do with the fix to the jump-thru behavior in the changelog for r79. If you can't wait, you can download a fixed runtime.js for the platform movement here, or just go back to using an old release (that's why they're there!). Unfortunately being a small team we can't afford a whole test lab to extensively verify every build before it goes out, so sometimes these things sometimes slip through the net and get released. If you are concerned about breaks in future you can simply wait a few days after a new release to make sure it's OK for production use. We've also been meaning to formally split releases in to stable and testing branches, but having a million things on our todo list and new features regularly being asked for, it's one of many things that's not quite done yet I'm afraid! But I think this case means it should be a new priority to get that branching sorted out.
I'm also going to have a look at the other new bug reports, hopefully it will just be straightforward to get fixed and release an update soon. Sorry again for the trouble and I hope r78 can tide you over in the mean time!