Hi, We've just upgraded from 2017.3 to 2018.1 Beta. We are running into next problem now. In VS Tools for Unity (3.4 on VS2015) the Unity projects do not want to build anymore: Error CS1703 Multiple assemblies with equivalent identity have been imported: 'C:\Program Files\Unity\Editor\Data\MonoBleedingEdge\lib\mono\4.7.1-api\Facades\System.Xml.XmlSerializer.dll' and 'C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6\Facades\System.Xml.XmlSerializer.dll'. Remove one of the duplicate references. UnityEditor.StandardEvents and the same error for many more of these System.xxx.dll assemblies. The Unity projects target .NET framework 4.6, just like the other self-made business assemblies that we put under the Plugins folder. In the Unity.csproj files, I notice that some references are indeed duplicated: <Reference Include="mscorlib"> <HintPath>C:\Program Files\Unity\Editor\Data\MonoBleedingEdge\lib\mono\4.6-api\mscorlib.dll</HintPath> </Reference> ... <Reference Include="mscorlib"> <HintPath>C:\Program Files\Unity\Editor\Data\MonoBleedingEdge\lib\mono\4.7.1-api\mscorlib.dll</HintPath> </Reference> However, there are more build errors listed than duplicates found in the .csproj Removing the duplicate references does not help, and next time when re-opening the Unity projects the duplicate references are back again. Anyone an idea what is going on? Thanks a lot.