"Consider app.config remapping of assembly ..." warning in F#

Below is I think a sample app.config that does what is suggested. However, what is in your project, and what FSharp.Core reference is there? Are you targeting .Net 4.5 or 4.0 or what? Does this project reference some older F# library? This typically is because two projects reference different versions of FSharp.Core.dll, e.g. check the <Reference> nodes in the .fsproj files.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
          <assemblyIdentity name="FSharp.Core" publicKeyToken="b03f5f7f11d50a3a"
                            culture="neutral"/>
<!--      <bindingRedirect oldVersion="0.0.0.0-2.9.9.9" newVersion="4.3.0.0"/>  -->
          <bindingRedirect oldVersion="2.0.0.0" newVersion="4.0.0.0"/>
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
</configuration>

same error related to Json.Net

In project file I had

<Reference Include="Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, processorArchitecture=MSIL">
   <SpecificVersion>False</SpecificVersion>
   <HintPath>..\packages\Newtonsoft.Json.6.0.1\lib\net45\Newtonsoft.Json.dll</HintPath>
</Reference>

and

<ItemGroup>
   <Reference Include="Newtonsoft.Json">
      <HintPath>..\packages\Newtonsoft.Json.5.0.6\lib\net45\Newtonsoft.Json.dll</HintPath>
   </Reference>
</ItemGroup>

Deleting the old one solved the problem.