I think the problem where that the <ProjectReference Include="..\..\an\other.csproj" /> where a x86 project and the failing project the <PlatformTarget>x86</PlatformTarget> in <PropertyGroup> where missing.

I assume that the reason that I only goth a MSB4236: The SDK "Microsoft.NET.Sdk" specified could not be found. is that the other project where still in the old format.

So basically I writhe this post just in case some on else (or I) get the same problem.