Wierd Build Error with XS on Mac

I've recently converted an application from java to C# using Xamarin. Currently, the project builds and runs on my Windows PC. However, when I try to build the same project on my Mac, I get the following build error:

/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets: Error: Tool exited with code: 138. Output:

I've done a couple of Google searches and nothing is coming up.

Any ideas what the problem could be?

EDITED: I've enabled diagnostic logging and have attached the build output.