After upgrading from 4.6.1 framework to 4.7.2 we started getting this error:
"The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'." and ultimately the solution was to add the "netstandard" assembly reference mentioned above:
<compilation debug="true" targetFramework="4.7.1" >
<assemblies>
<add assembly="netstandard, Version=2.0.0.0, Culture=neutral,
PublicKeyToken=cc7b13ffcd2ddd51"/>
</assemblies>
</compilation>