unable to bind dropdownlist in mvc using viewmodel property In my viewmodel I've a getter property as below. 
    [Display(Name = "Users System:")]
    public string UsersSystem { get; set; }


    public IEnumerable<SelectListItem> SystemsList
    {
get
{
List<SelectListItem> lst = new List<SelectListItem>();
string[] UsersSystem = ConfigurationManager.AppSettings["UsersSystem"].ToString().Split(new char[] { ',' });
foreach (var item in UsersSystem)
{
lst.Add(new SelectListItem { Text = item, Value = item });
}

return lst;
}
    }

I need to bind the values to a dropdownlist but I m getting Object reference not set to an instance of an object. My view has the following mark up
 @model GazetteerAddressRequest.Lib.Model.ChangeRequestModel

 @Html.DropDownListFor(model => model.UsersSystem, Model.SystemsList , new { @class = "form-control" })

Any ideas? thanks

As Stephen has mentioned you can't use the same name for the model property and the SelectList. Add a new property in ChangeRequestModel to hold the value of the selected item in the Dropdown. 
public string UserSystemSelected { get; set; }

In your View 
@Html.DropDownListFor(model => model.UserSystemSelected, Model.UsersSystem, new { @class = "form-control" })

Here you are populating the dropdown with Model.UsersSystem which has the list of all the SelectListItem and the VALUE SELECTED from the dropdown gets binded to UserSystemSelected.
EDIT:
You can also try this:
In your controller, inside the Action method
ViewBag.SystemList = new SelectList(
ConfigurationManager.AppSettings["UsersSystem"].ToString()
.Split(',')
.Select(x => new KeyValuePair<string, string>(x, x)),"Key", "Value");

And in your View
Html.DropDownListFor(m => m.UserSystemSelected, (SelectList)ViewBag.SystemList)


You have to pass the model into view, otherwise the model will be null in view. 
Eg. first you can pass the SelectListItem list into ChangeRequestModel and then that into the view.
public ActionResult YourPage(){
    return View(changeRequestModel);
}