Getting Error in PhysicalApplicationPath

Case 1

Let's see the code shown in the following: 

string rootPath = ConfigurationManager.AppSettings["FilePath"];
var currentApplicationPath = HttpContext.Current.Request.PhysicalApplicationPath;
var provider = new MultipartFormDataStreamProvider(currentApplicationPath + "\\tempUploads");
try{

     await Request.Content.ReadAsMultipartAsync(provider);

   }
catch(Exception ex)

{

   throw ex;

}

Here i am passing from header Accept: tex/json.

I am getting error. with used above code, error shown in the following screenshot:

 

Case 2

If I used MultipartFormDataStreamProvider with app ConfigurationManager.AppSettings["FilePath"] than I was successfully execute my code.

string rootPath = ConfigurationManager.AppSettings["FilePath"];
var provider = new MultipartFormDataStreamProvider(ConfigurationManager.AppSettings["FilePath"])

try{

    await Request.Content.ReadAsMultipartAsync(provider);

}
catch(Exception ex)

{

   throw ex;

}