System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies

I am trying to make an Elastic connection but its throwing error

I tried to modify the web config and also developer cmd for adding the dll but non of them is working for me. Please help me in resoplving this issue

2.gacutil -I "Bin\System.Runtime.CompilerServices.Unsafe.dll" Not working.

ConnectionToEs connectionToEs = new ConnectionToEs();

    var response = connectionToEs.EsClient().Search<LockupReport>(s => s
                    .Query(q => q
                    .MatchAll()
                    ));
    var dataobj = response.Documents;