Adding users to roles on registring failed ASP.NET

I like to enable users to choose their role on register in asp.net mvc web application. I have previous add roles via asp.net addministration tool. Here is the code I am using in register methods

public ActionResult Register()  
{
ViewData["roleName"] = new SelectList(Roles.GetAllRoles(), "roleName");
return View();
}


 [HttpPost]
    public ActionResult Register(RegisterModel model)
    {
        if (ModelState.IsValid)
        {
            // Attempt to register the user
            MembershipCreateStatus createStatus;
            Membership.CreateUser(model.UserName, model.Password, model.Email, null, null, true, null, out createStatus);

            if (createStatus == MembershipCreateStatus.Success)
            {
                Roles.AddUserToRole(model.UserName, "roleName");
                FormsAuthentication.SetAuthCookie(model.UserName, false /* createPersistentCookie */);
                return RedirectToAction("Index", "Home");
            }
            else
            {
                ModelState.AddModelError("", ErrorCodeToString(createStatus));
            }
        }

        // If we got this far, something failed, redisplay form
        return View(model);
    }

While in Register View I got this code

    <label for="roleName">Select Role:</label>
         @Html.DropDownList("roleName")
         @Html.ValidationMessage("roleName")

Roles are written in the database and users although. However UsersInRoles table is empty and I got this exception

System.Configuration.Provider.ProviderException: The role 'roleName' was not found.

Does anybody had the same problem?

You should add roleName parameter to Register controller action for get selected by user roleName, or retrieve roleName from FormCollection, here is example Change your Register post action to:

        [HttpPost]
        public ActionResult Register(RegisterModel model, String roleName)
        {
            if (ModelState.IsValid)
            {
                // Attempt to register the user
                MembershipCreateStatus createStatus;
                Membership.CreateUser(model.UserName, model.Password, model.Email, null, null, true, null, out createStatus);

                if (createStatus == MembershipCreateStatus.Success)
                {
                    Roles.AddUserToRole(model.UserName, roleName);
                    FormsAuthentication.SetAuthCookie(model.UserName, false /* createPersistentCookie */);
                    return RedirectToAction("Index", "Home");
                }
                else
                {
                    ModelState.AddModelError("", ErrorCodeToString(createStatus));
                }
            }

            // If we got this far, something failed, redisplay form
            return View(model);
        }