Hi,
Thanks for sharing this issue.
The problem appears to be a compatibility issue between SpecFlow and VS2015.
When NCrunch loads your project, it detects the reference to the SpecFlow binary and automatically includes the SpecFlow.targets file inside your project as an import. The reason for this is to allow NCrunch to be able to regenerate SpecFlow tests every time it builds your project, which is something that won't happen without this targets file included.
So it's the SpecFlow test/step generation that is causing the build to fail. I'm not sure how heavily you're using SpecFlow, but I expect that this issue may be a major one for you regardless of whether or not you use NCrunch. I recommend reporting it to them.
If you'd like to make your NCrunch build work in the same way as the Visual Studio build (and by-pass the error), open up the TechTalk.SpecFlow.targets file inside your Nuget packages directory, find the 'GenerateAll' task invocation on line 47, and comment it out. For example:
<Target Name="UpdateFeatureFilesInProject" DependsOnTargets="BeforeUpdateFeatureFilesInProject">
<!-- GenerateAll
ShowTrace="$(ShowTrace)"
BuildServerMode="$(BuildServerMode)"
OverwriteReadOnlyFiles="$(OverwriteReadOnlyFiles)"
ProjectPath="$(MSBuildProjectFullPath)"
ForceGeneration="$(ForceGeneration)"
VerboseOutput="$(VerboseOutput)">
<Output TaskParameter="GeneratedFiles" ItemName="SpecFlowGeneratedFiles" />
</GenerateAll -->
</Target>