This is from gitter chat in Mono: https://gitter.im/mono/mono

Any idea why we are getting "invalid image" error from VS solution file under certain conditions? Seems to be working under .NET Core and .NET Framework, but not Mono.

https://travis-ci.org/pythonnet/pythonnet/jobs/415741698#L1874

Currently running NuGet.exe 4.1.0.
Updating NuGet.exe to 4.7.1.
Update successful.
MSBuild auto-detection: using msbuild version '15.0' from '/usr/lib/mono/msbuild/15.0/bin'.
Error parsing solution file at /home/travis/build/pythonnet/pythonnet/pythonnet.sln: Invalid Image

Katelyn Gadd @kg 22:36
invalid image parsing sln makes it sound like it's having trouble loading msbuild assemblies
#3282 this is the same error message
rather, the first part is the same. different exception
so it is indeed caused by a managed exception
rainersigwald@7960c80#diff-af08e5d2c5235a664572f4581ba0e7c6R161 it looks like msbuild has had mono compatibility issues before

Denis Akhiyarov @denfromufa 22:41
@kg thanks for diagnostics, any easy workaround the get the CI builds going? I don't recall these errors last week for the same build configuration:
https://travis-ci.org/pythonnet/pythonnet/builds/413267958

Katelyn Gadd @kg 22:42
i'm sorry, i don't know enough to recommend a solution right now. you might want to ping @rainersigwald to see if he has any ideas
or you could file an issue since it's an exception in msbuild to see if they can suggest a fix. i think that error message is insufficient
so it is a useful defect report in the sense of 'we should at least improve this error message'
it looks like it only outputs exc.Message which is insufficient in this case