Gimp not working after os update

[lemonphenomenon]

I have used Gimp, version 2.8.0, on my desktop mac, OS 10.8 (mountain lion), for several years. Yesterday I updated my operating system to 10.12.5 and now Gimp doesn't work. I get a message saying, weirdly, that Gimp cannot open Gimp-format files. My X-Quartz is version 2.7.2

Has anyone any idea what the problem might be and how to remedy it?

Thanks

I have now updated XQuartz to 2.7.11, but it hasn't made any difference.