Specifically for StackOverflow Question - http://stackoverflow.com/q/15560855/124069

StackoverflowQuestion15560855.cs

public ActionResult LogOn(LogOnModel model, string returnUrl)
{
    // check if a valid user was selected
    var user = GetuserByname(model.UserName);

    if (user.ToList().Count != 1)
    {   
        ModelState.AddModelError("Username", "Username is invalid");   
    }

    var dbPassword = user.First().UserPassword.ToString().Trim();
    var enterPassword = CreatePasswordHash(model.Password, user.First().Salt.ToString().Trim());

    if (dbPassword != enterPassword)
    {
        ModelState.AddModelError("dbPassword", "Password is invalid");
    }
    
    if (!ModelState.IsValid) {   
        return View(model);    
    }
    
    FormsAuthentication.SetAuthCookie(user.First().tblUserRole.RoleName, model.RememberMe);
    Session["logged"] = user.First().Username;

    string roleName = user.First().tblUserRole.RoleName;
    Roles.AddUserToRole(model.UserName, roleName);
    
    return RedirectToAction("Index", "Home");
}

This is just a modification of the original code posted. It's modified to clean up the Cyclomatic Complexity... just a little bit. Deeply nested if statements kinda get under my skin.

I hope this is helpful.