MVC app doesn't run with a generic method

I wanted to create a method in my Base controller that would take a list and return it as a SelectList. I wrote a method, and the site compiles, but I get this message:

Cannot call action method 'System.Collections.Generic.IEnumerable1[System.Web.Mvc.SelectListItem] GetSelectList[T](System.Collections.Generic.IEnumerable1[T], System.String, System.String, System.String, System.Object)' on controller 'PublicationSystem.Controllers.BaseController' because the action method is a generic method.
Parameter name: methodInfo

I'm wondering what I did wrong. Here's the code:

public partial class BaseController : Controller
{
    public IEnumerable<SelectListItem> GetSelectList<T>
    (
        IEnumerable<T> itemList, 
        string textField,
        string valueField,
        string defaultPrompt = "", 
        object defaultValue = null)
    {
        IEnumerable<SelectListItem> returnList = null;

        if (!string.IsNullOrEmpty(defaultPrompt))
        {
            returnList = Enumerable.Repeat(
                new SelectListItem { Value = (string)defaultValue, Text = defaultPrompt },
                count: 1);
        }

        var textProp = typeof (T).GetProperty(textField);
        var valueProp = typeof (T).GetProperty(valueField);

        returnList = returnList.Concat
            (itemList
                .Select(x =>
                    new SelectListItem
                    {
                        Value = Convert.ToString(valueProp.GetValue(x)),
                        Text = Convert.ToString(textProp.GetValue(x)),
                    }).Distinct().ToList());

        return returnList.ToList();
    }
}

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
        routes.LowercaseUrls = true;
        routes.MapMvcAttributeRoutes(); // Errors here
        //..
    }
}