ASP.Net Core MVC Error: There is already an open DataReader associated with this Connection which must be closed first

Just learn ASP.NET Core Identity and try to apply.

But I got this There is already an open DataReader associated with this Connection which must be closed first.

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    string connectionString = Configuration.GetConnectionString("default");
    services.AddDbContext<AppDBContext>(c => c.UseSqlServer(connectionString));
    services.AddIdentity<IdentityUser, IdentityRole>().AddEntityFrameworkStores<AppDBContext>();
    services.ConfigureApplicationCookie(options =>
    {
        options.LoginPath = "/Account/Login";
    });

    services.AddMvc().AddJsonOptions(o =>
    {
        o.JsonSerializerOptions.PropertyNamingPolicy = null;
        o.JsonSerializerOptions.DictionaryKeyPolicy = null;
    });

    services.AddControllersWithViews();
}

AdministrationController

namespace IspdHelpDesk.Controllers
{
    public class AdministrationController : Controller
    {
        private readonly RoleManager<IdentityRole> roleManager;
        private readonly UserManager<IdentityUser> userManager;
        private readonly ILogger<AdministrationController> logger;

        public AdministrationController(RoleManager<IdentityRole> roleManager,
                                        UserManager<IdentityUser> userManager,
                                        ILogger<AdministrationController> logger)
        {
            this.roleManager = roleManager;
            this.userManager = userManager;
            this.logger = logger;
        }

        [HttpGet]
        public IActionResult CreateRole()
        {
            return View();
        }

        [HttpPost]
        public async Task<IActionResult> CreateRole(CreateRoleViewModel model)
        {
            if (ModelState.IsValid)
            {
                IdentityRole identityRole = new IdentityRole
                {
                    Name = model.RoleName
                };

                IdentityResult result = await roleManager.CreateAsync(identityRole);

                if (result.Succeeded)
                {
                    return RedirectToAction("ListRoles", "Administration");
                }

                foreach (IdentityError error in result.Errors)
                {
                    ModelState.AddModelError("", error.Description);
                }


            }

            return View(model);
        }

        [HttpGet]
        public IActionResult ListRoles()
        {
            var roles = roleManager.Roles;
            return View(roles);
        }


        [HttpGet]
        public async Task<IActionResult> EditRole(string id)
        {
            var role = await roleManager.FindByIdAsync(id);

            if (role == null)
            {
                ViewBag.ErrorMessage = $"Role with Id = {id} cannot be found";
                return View("NotFound");
            }

            var model = new EditRoleViewModel
            {
                Id = role.Id,
                RoleName = role.Name
            };

            foreach (var user in userManager.Users)
            {
                if (await userManager.IsInRoleAsync(user, role.Name))
                {
                    model.Users.Add(user.UserName);
                }
            }

            return View(model);
        }
    }
}

How to solve - There is already an open DataReader associated with this Connection which must be closed first ?