将用户添加到asp.net mvc 4.5中的角色时，出现错误-“未找到用户（用户名）”

Question

Here is my account login controller. (My "auth" class method returns "user" or "admin" and is logged in accordingly).

[HttpPost]
    public ActionResult Login(string userName, string pass)
    {
        Auth auth = new Auth();
        if (auth.MyAuth(userName) == "user")
        {
            FormsAuthentication.SetAuthCookie(userName, true);
            return RedirectToAction("Index", "Home");
        }

        else if(auth.MyAuth(userName) == "admin")
        {
            FormsAuthentication.SetAuthCookie(userName, true);
            if (!Roles.RoleExists("admin"))
            {
                Roles.CreateRole("admin");
            }
            if (!Roles.IsUserInRole(userName, "admin"))
            {
                Roles.AddUserToRole(userName, "admin");
            }

            RedirectToAction("Index", "Home");
        }
        return RedirectToAction("Login");
    }

Edited

public class Auth 
{ 
  public string MyAuth(string userName) 
  { if (userName.Length == 4) 
     { return "user"; } 
    else if (userName.Length == 5) 
      { return "admin"; } 
    return "unauth"; } }

The problem is when I add a user with Roles.AddUserToRole(userName, "admin"), I get an error that it cannot find user(userName). I'm at a loss as to why!

Here's the role manager details from web.config:

<roleManager enabled="true" defaultProvider="DefaultRoleProvider">
<providers>
<add name="DefaultRoleProvider" 
  type="System.Web.Providers.DefaultRoleProvider, System.Web.Providers,
  Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" 
  connectionStringName="DefaultConnection" applicationName="/" />
</providers>
</roleManager>

Answer 1

The problem is you are not setting roleManager properly in webconfig. change your webconfig as below.

 <roleManager enabled="true" 
cacheRolesInCookie="true" 
cookieName=".ASPXROLES" 
cookieTimeout="30" 
cookiePath="/" 
cookieRequireSSL="false" 
cookieSlidingExpiration="true" 
cookieProtection="All" 
defaultProvider="AspNetSqlRoleProvider"
 createPersistentCookie="false" maxCachedResults="25" />