invalid object name dbo.IdentityUserRole

Hi!
I have two problems. Both are with the dbo.IdentityUserRole. If I don't override the 
protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<IdentityUserRole>().HasKey(r => new { r.RoleId, r.UserId }); } method, I get this error: IdentityUserRole has no key defined.
If I override it, then I get "invalid object name dbo.IdentityUserRole" inner exception in this code(IdentityResult res...):
protected async void registerButton_Click(object sender, EventArgs e){ UserStore<Client> _userStore = new UserStore<Client>(SITCContext.Create()); UserManager<Client> manager = new UserManager<Client>(_userStore); IdentityResult res = await manager.CreateAsync(item, PasswordID.Text); //...} What should I change in the code?
Thanks!