Assembly conflicts after install Microsoft.ReportingServices.ReportViewerControl.WebForms - asp.net-mvc

Question

I have assembly conflicts that I can't solve (or understand) after I've upgraded to ReportViewer 14.0 in an existing MVC-project.
Warning Found conflicts between different versions of the same dependent assembly.
In Visual Studio, double-click this warning (or select it and press Enter) to fix the conflicts; otherwise, add the following binding redirects to the
"runtime" node in the application configuration file:
NRM C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\Microsoft.Common.CurrentVersion.targets 1964
It also says:
No way to resolve conflict between
"Microsoft.Build.Framework, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and
"Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".
If I double-click the error message (as it says) it adds these lines to Web.Config:
<dependentAssembly>
<assemblyIdentity name="Microsoft.Build.Framework" publicKeyToken="B03F5F7F11D50A3A" culture="neutral"/>
<bindingRedirect oldVersion="0.0.0.0-14.0.0.0" newVersion="14.0.0.0"/>
</dependentAssembly>
But this creates this error at runtime:
Could not load file or assembly 'Microsoft.Build.Framework,
Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or
one of its dependencies. The system cannot find the file specified.
If I remove the bindingRedirect in Web.Config I only have the warning but all (including ReportViewer 14.0) works fine.
When I change Build-out to Diagnostic, I receive this extra information:
1> There was a conflict between "Microsoft.Build.Framework, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". (TaskId:13)
1> No way to resolve conflict between "Microsoft.Build.Framework, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". Choosing "Microsoft.Build.Framework, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" arbitrarily. (TaskId:13)
1> References which depend on "Microsoft.Build.Framework, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" [C:\Program Files (x86)\Reference Assemblies\Microsoft\MSBuild\v14.0\Microsoft.Build.Framework.dll]. (TaskId:13)
1> C:\Program Files (x86)\Reference Assemblies\Microsoft\MSBuild\v14.0\Microsoft.Build.Tasks.Core.dll (TaskId:13)
1> Project file item includes which caused reference "C:\Program Files (x86)\Reference Assemblies\Microsoft\MSBuild\v14.0\Microsoft.Build.Tasks.Core.dll". (TaskId:13)
1> Microsoft.ReportViewer.Design, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
1> Microsoft.ReportViewer.WebDesign, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
1> C:\Program Files (x86)\Reference Assemblies\Microsoft\MSBuild\v14.0\Microsoft.Build.Utilities.Core.dll (TaskId:13)
1> Project file item includes which caused reference "C:\Program Files (x86)\Reference Assemblies\Microsoft\MSBuild\v14.0\Microsoft.Build.Utilities.Core.dll". (TaskId:13)
1> Microsoft.ReportViewer.Design, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
1> Microsoft.ReportViewer.WebDesign, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
1> References which depend on "Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" [C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6.2\Microsoft.Build.Framework.dll]. (TaskId:13)
1> D:\Dev\VS\--hidden-- (MVC)\NRM\packages\Microsoft.ReportingServices.ReportViewerControl.WebForms.140.340.80\lib\net40\Microsoft.ReportViewer.WebForms.dll (TaskId:13)
1> Project file item includes which caused reference "D:\Dev\VS\--hidden-- Relatie Management (MVC)\NRM\packages\Microsoft.ReportingServices.ReportViewerControl.WebForms.140.340.80\lib\net40\Microsoft.ReportViewer.WebForms.dll". (TaskId:13)
1> Microsoft.ReportViewer.WebDesign, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
1> Microsoft.ReportViewer.WebForms, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91, processorArchitecture=MSIL (TaskId:13)
In the diagnostic log, there are also conflicts mentioned for:
System.Net
Microsoft.Build.Framework
mscorlib
System.Core
System

Answer 1

I got the error today again.
It happened when I added ReportViewer through NuGet while I had added those reference in the past manually. I cleared the manual reference but this didn't clear the Web.Config enough. In the process I also updated other packages which might have to do with it.
I solved the issue by cleaning these lines from Web.Config.