Editor crashes on launch: filename not found [in UE4Editor-Core.dylib]

I have an iMac (Retina 5k, 27-inch, Late 2014), 4 GHz Intel Core i7, 32 GB 1600 MHz DDR3, AMD Radeon R9 M295X 4096 MB.

I’ve never been able to open the editor. It always crashes on startup with the following error:


link text

My filesystem is not case sensitive.

Any ideas?