Question

I get this error whenever I submit the form also the action method is not being called because of this:

ArgumentException: An item with the same key has already been added.

And the exception details:

[ArgumentException: An item with the
same key has already been added.]
System.ThrowHelper.ThrowArgumentException(ExceptionResource
resource) +52
System.Collections.Generic.Dictionary`2.Insert(TKey
key, TValue value, Boolean add)
+9382923 System.Linq.Enumerable.ToDictionary(IEnumerable`1
source, Func`2 keySelector, Func`2
elementSelector, IEqualityComparer`1
comparer) +252
System.Linq.Enumerable.ToDictionary(IEnumerable`1
source, Func`2 keySelector,
IEqualityComparer`1 comparer) +91
System.Web.Mvc.ModelBindingContext.get_PropertyMetadata()
+228 System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext
controllerContext, ModelBindingContext
bindingContext, PropertyDescriptor
propertyDescriptor) +392
System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext
controllerContext, ModelBindingContext
bindingContext) +147
System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext
controllerContext, ModelBindingContext
bindingContext, Object model) +98
System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext
controllerContext, ModelBindingContext
bindingContext) +2504
System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext
controllerContext, ModelBindingContext
bindingContext) +548
System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext
controllerContext, ParameterDescriptor
parameterDescriptor) +473
System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext
controllerContext, ActionDescriptor
actionDescriptor) +181
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext
controllerContext, String actionName)
+830 System.Web.Mvc.Controller.ExecuteCore()
+136 System.Web.Mvc.ControllerBase.Execute(RequestContext
requestContext) +111
System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext
requestContext) +39
System.Web.Mvc.<>c__DisplayClass8.b__4()
+65 System.Web.Mvc.Async.<>c__DisplayClass1.b__0()
+44 System.Web.Mvc.Async.<>c__DisplayClass8`1.b__7(IAsyncResult
_) +42 System.Web.Mvc.Async.WrappedAsyncResult`1.End()
+141 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult
asyncResult, Object tag) +54
System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult
asyncResult, Object tag) +40
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult
asyncResult) +52
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult
result) +38
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
+8836913 System.Web.HttpApplication.ExecuteStep(IExecutionStep
step, Boolean& completedSynchronously)
+184

ViewPage

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/XYZ.Master"
    Inherits="System.Web.Mvc.ViewPage<XYZ.Models.Admin.AdminSegmentCommissionsModel>" %>
    <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
        Create
    </asp:Content>
    <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
        <% using (Html.BeginForm()) {%>    
            <div class="box3">
                <div class="userinfo">
                    <h3>Admin Segment Commissions</h3>
                </div>
                <div class="buttons-panel">
                    <ul>
                       <li>
                           <input type="submit" value="Save" class="save" />
                       </li>
                       <li>
                           <%:Html.ActionLink("Cancel", "Index", new { controller = "AdminSegmentCommissions" }, new { @class = "cancel" })%>
                           <%--<input type="button" value="Cancel" class="cancel" onclick="document.location.href='/AirlineLedgerTransactionReceiver/Index'" />--%>
                       </li>
                   </ul>
               </div>
           </div>
           <div class="row-1">
               <div class="form-box1 round-corner">
                   <div class="form-box1-row">
                       <div class="form-box1-row-content float-left">
                           <div>
                               <label>
                                   <%: Html.LabelFor(model => model.FromSegmentNumber) %></label>
                                   <%: Html.TextBoxFor(model => model.FromSegmentNumber) %>
                                   <%: Html.ValidationMessageFor(model => model.FromSegmentNumber) %>
                          </div>
                      </div>
                  </div>
              </div>
          </div>
      <%} %>

</asp:Content>
<asp:Content ID="Content3" ContentPlaceHolderID="CssContent" runat="server">
</asp:Content>
<asp:Content ID="Content4" ContentPlaceHolderID="JSContent" runat="server">
</asp:Content>

Answer 1

Most likely, you have model which contains the same property twice. Perhaps you are using new to hide the base property.

Solution is to override the property or use another name.

If you share your model, we would be able to elaborate more.