Error adding item with same key when submit

I'd like to solve it as soon as possible.

Environment: Asp.Net MVC4 (cshtml)

I would like to post the viewmodel bound to view on submit to the stovetoller.

An item containing the same key has already been added. '/' An application server error occurs.

I don't know what's wrong, so could someone tell me?

@model namespace.ViewModels.SampleViewModel
...omitted...
@using(Html.BeginForm("Index", "Controller Name", FormMethod.Post))
{
    ...omitted...

    <td><input type="submit" value="Registration"/>/td>

}

// Initial View
[HttpGet]
public ActionResult Index (stringdType)
{
    varViewModel=new Sample ViewModel();

    … (all set in ViewModel) …

    return View (ViewModel);
｝

// registration
[HttpPost]
public ActionResult Index (sample ViewModel vm)
{
    ...omitted...
}

Thank you for your cooperation.

c# asp.net mvc

2022-09-30 16:42