UE4 Crashes on startup (Mac)

I have a very strange issue with a project I’m working on. I didn’t have any problems opening it up and suddenly one day, as I got the latest revision, every time I open it it crashes and shows me this error I pasted below. The programmer says he hasn’t removed or added anything that might cause this. I am working on Unreal version 4.6.1 and final version of Mac Yosemite. Do you have any idea how to fix this? It would be greatly appreciated.

Any ideas?

Hi ,

Thanks for submitting your crash using the Crash Reporter. Using that information I was able to file the following report: JIRA [UE-9523] This will greatly aid our developers in pinpointing the cause of the crash, at which point an update will be added to this post…

This has been reported as fixed. Please try opening in the latest preview and let us know if you have better results.