Could not load file or assembly 'SendGrid, Version=9.10.0.0

I am attempting to hookup SendGrid for automated account confirmation and password recovery. I am using ASP.net webform application and c#. I have installed the NuGet SendGrid package. I am attempting to amend the IdentityConfig.cs file.

The package builds ok. When I register a new user I get the following error: Could not load file or assembly 'SendGrid, Version=9.10.0.0, Culture=neutral, PublicKeyToken=4f047e93159395ca' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

However, the user does get added to the ASPNetUsers database table.

As always, I am very grateful for any help. My code is:

using System;
using System.Security.Claims;
using System.Threading.Tasks;
using Microsoft.AspNet.Identity;
using Microsoft.AspNet.Identity.EntityFramework;
using Microsoft.AspNet.Identity.Owin;
using Microsoft.Owin;
using Microsoft.Owin.Security;
using SendGrid.Models;
using SendGrid.Helpers.Mail;
using System.Collections.Generic;

namespace SendGrid
{
public class EmailService : IIdentityMessageService
{
    public async Task SendAsync(IdentityMessage message)
    {
        await configSendGridasync(message);
    }

    // Use NuGet to install SendGrid (Basic C# client lib) 
    private async Task configSendGridasync(IdentityMessage message)
    {
        var apiKey = System.Web.Configuration.WebConfigurationManager.AppSettings["SendGrid_API_Key"];
        var client = new SendGridClient(apiKey);
        var msg = new SendGridMessage();

        msg.SetFrom(new EmailAddress("azure_test@azure.com", "Me"));

        msg.AddTo(message.Destination);

        msg.SetSubject("Testing the SendGrid C# Library");

        msg.AddContent(MimeType.Text, "Hello World plain text!");
        msg.AddContent(MimeType.Html, "<p>Hello World!</p>");

        var response = await client.SendEmailAsync(msg);

        // Create a Web transport for sending email.
        //var transportWeb = new Web(credentials);

        //// Send the email.
        //if (transportWeb != null)
        //{
        //    await transportWeb.DeliverAsync(msg);
        //}
        //else
        //{
        //    Trace.TraceError("Failed to create Web transport.");
        //    await Task.FromResult(0);
        //}
    }
}