The easiest way to reproduce is to have a PC with only VS2017 installed

Reproduction steps:
1. Open the attached project
2. Try to build to UWP
3. Builds as expected
4. Try to build to SDK 8.1
5. Compilation will fail because only VS2017 is installed
6. Now switch back and try to build to UWP once again
7. Fails with following output (from Editor.log):

(Filename: /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs Line: 514)

- Finished compile Library/ScriptAssemblies/Assembly-CSharp.dll
Compilation failed because the compiler couldn't be executed!

(Filename: Line: 21)

DisplayProgressNotification: Build Failed
Error building Player because scripts had compiler errors

Notes:
- Sometimes not reproducible and everything works as expected, but fails in 90% of cases.
- If you remove "ArrayList" from the script in the project - everything works fine.
- Workaround: Re-import all