Partial view throwing error

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ASP.NET

Ajax

MVC5

Pagination using AJAX(I made a PartialView so page is not going to refresh every time when yser click Next button to view next record)
While retrieving Data from 1 table it works perfectly fine,but it throws error while fetching data from 2 tables using navigational properties when click Next button :" An error occurred while executing the command definition "

Anyone has any idea where im doing wrong?

What I have tried:

Controller :

I wrote this code in Index() ------ This is HttpGet

var tsk = db.Tasks.Include(e => e.Customers);
 ViewBag.CurrentPage = 1;
 ViewBag.LastPage = Math.Ceiling(Convert.ToDouble(tsk.ToList().Count)/5);
 return View(tsk.Take(5));

And for HttpPost Index ()

 ViewBag.CurrentPage = CurrentPage;
 ViewBag.LastPage = LastPage;
return PartialView("_Task", db.Tasks.OrderBy(v => v.TaskID).Skip((CurrentPage - 1) * 5).Take(5));

View :

<div style="width: 600px;">
      @Html.ActionLink("Add Task", "Create", "Home", null)
      <div id="TaskDiv">
          @Html.Partial("_Task", Model)
      </div>
  </div>
  <div>
      @using (Ajax.BeginForm(new AjaxOptions { HttpMethod = "POST", InsertionMode = InsertionMode.Replace, UpdateTargetId = "TaskDiv" }))
      {
          <input type="hidden" id="CurrentPage" name="CurrentPage" value="@ViewBag.CurrentPage" />
          <input type="hidden" id="LastPage" name="LastPage" value="@ViewBag.LastPage" />
      }
      <input type="button" id="Previous" value="Previous" />
      <input type="button" id="Next" value="Next" />
  </div>

I also wrote some JQuery and JS code

Partial View

<tbody>
        @foreach (var item in Model)
        {
            <tr>
                <td>@item.Customers.Name</td> // Using IEnumerable Task Model // Throw error here when clicking Next Button 
                <td>@item.Name</td>
                <td>@item.StartDate</td>
                <td>@item.EndDate</td>
                <td>Aagent Name</td>
                <td>Status</td>
            </tr>
        }
    </tbody>