How to update data in multiple tables at same time in mvc

Question

Here I am able to add the data in more than one table. Let i have 3 tables User, Franchise and Fee.

I am not able to update the data in more than one table,it throwing the exception:

public MessageResult SaveAndUpdateFranchisee(UserViewModel model) {
 var result = new MessageResult();
 try {
  User userData = new User();
  Franchise franchiseData = new Franchise();
  var ExistUser = db.Users.Where(a => a.Id == model.Id).FirstOrDefault(); //Update record
  if (model.Id > 0) {
   Fee feeData = new Fee {
    FranchiseeFee = model.FranchiseeFee, PaymentTermsFranchiseFee = model.PaymentTermsFranchiseFee, EquipmentCost = model.EquipmentCost, PaymentTermsEquipmentCost = model.PaymentTermsEquipmentCost, OtherFee = model.OtherFee, PaymentTermsOtherFee = model.PaymentTermsOtherFee, ConsumableStock = model.ConsumableStock, PaymentTermsConsumableStock = model.PaymentTermsConsumableStock, FrozenFoodStock = model.FrozenFoodStock, PaymentTermsFrozenFoodStock = model.PaymentTermsFrozenFoodStock, TotalAmountDue = model.TotalAmountDue, TotalAmountPaid = model.TotalAmountPaid, BalanceAmount = model.BalanceAmount, LoyaltyFeePercentage = model.LoyaltyFeePercentage, FixedMonthlyFee = model.FixedMonthlyFee, Note = model.Note, UserId = model.CurrentUserId, LOIDocUrl = model.LOIDocUrl, ModifiedDate = DateTime.Now
   };
   ExistUser.Email = model.Email;
   //var pwd = SecutiryServices.EncodePasswordToBase64(model.Password);
   //userData.Password = pwd;ExistUser.Password = model.Password;
   ExistUser.FirstName = model.FirstName;
   ExistUser.MiddleName = model.MiddleName;
   ExistUser.LastName = model.LastName;
   ExistUser.FullName = model.FullName;
   ExistUser.MobileNo = model.MobileNo;
   ExistUser.ModifyDate = DateTime.Now;
   franchiseData.Name = model.FullName;
   franchiseData.MobileNo = model.MobileNo;
   franchiseData.AlternateNo = model.AlternetNo;
   franchiseData.CompanyPhoneNo = model.PhoneNo;
   franchiseData.Address = model.Address;
   franchiseData.City = model.City;
   franchiseData.State = model.State;
   franchiseData.PinCode = model.PinCode;
   franchiseData.CompanyName = model.CompanyName;
   franchiseData.CompanyAddress = model.CompanyAddress;
   franchiseData.CompanyCity = model.CompanyCity;
   franchiseData.CompanyState = model.CompanyState;
   franchiseData.CompanyAddress = model.CompanyAddress;
   franchiseData.CompanyPinCode = model.CompanyPinCode;
   franchiseData.ModifiedDate = DateTime.Now;
   userData.Franchises.Add(franchiseData);
   foreach(var item in userData.Franchises) {
    item.Fees.Add(feeData);
   }
   db.Users.Attach(userData);
   db.Entry(userData).State = System.Data.Entity.EntityState.Modified;
   //db.Users.Add(userData);
   db.SaveChanges();
   result.Message = "Your franchise has been updated successfully..";
   result.Status = true;
  }
  //For Insert recored..
  else {
   Fee feeData = new Fee {
    FranchiseeFee = model.FranchiseeFee, PaymentTermsFranchiseFee = model.PaymentTermsFranchiseFee, EquipmentCost = model.EquipmentCost, PaymentTermsEquipmentCost = model.PaymentTermsEquipmentCost, OtherFee = model.OtherFee, PaymentTermsOtherFee = model.PaymentTermsOtherFee, ConsumableStock = model.ConsumableStock, PaymentTermsConsumableStock = model.PaymentTermsConsumableStock, FrozenFoodStock = model.FrozenFoodStock, PaymentTermsFrozenFoodStock = model.PaymentTermsFrozenFoodStock, TotalAmountDue = model.TotalAmountDue, TotalAmountPaid = model.TotalAmountPaid, BalanceAmount = model.BalanceAmount, LoyaltyFeePercentage = model.LoyaltyFeePercentage, FixedMonthlyFee = model.FixedMonthlyFee, Note = model.Note, UserId = model.CurrentUserId, LOIDocUrl = model.LOIDocUrl, CreatedDate = DateTime.Now
   };
   userData.Email = model.Email;
   //var pwd = SecutiryServices.EncodePasswordToBase64(model.Password);
   //userData.Password = pwd;userData.Password = model.Password;
   userData.FirstName = model.FirstName;
   userData.FullName = model.FirstName + " " + model.LastName;
   userData.LastName = model.LastName;
   userData.MobileNo = model.MobileNo;
   userData.IsActive = true;
   userData.IsDelete = false;
   userData.CreatedDate = DateTime.Now;
   userData.UserTypeId = 2;
   franchiseData.CompanyId = model.CurrentUserId;
   franchiseData.Name = userData.FullName;
   franchiseData.MobileNo = model.MobileNo;
   franchiseData.AlternateNo = model.AlternetNo;
   franchiseData.Address = model.Address;
   franchiseData.City = model.City;
   franchiseData.State = model.State;
   franchiseData.PinCode = model.PinCode;
   franchiseData.CompanyName = model.CompanyName;
   franchiseData.CompanyPhoneNo = model.PhoneNo;
   franchiseData.CompanyAddress = model.CompanyAddress;
   franchiseData.CompanyCity = model.CompanyCity;
   franchiseData.CompanyState = model.CompanyState;
   franchiseData.CompanyAddress = model.CompanyAddress;
   franchiseData.CompanyPinCode = model.CompanyPinCode;
   franchiseData.CreatedDate = DateTime.Now;
   franchiseData.IsActive = true;
   userData.Franchises.Add(franchiseData);
   foreach(var item in userData.Franchises) {
    item.Fees.Add(feeData);
   }
   db.Users.Add(userData);
   db.SaveChanges();
   //db.AddUserRole(userData.Id, 4);
   result.Message = "Your franchisee has been created successfully..";
   result.Status = true;
  }
  return result;
 } catch (Exception ex) {
  result.Message = "We are unable to process your request at this time. Please try again later.";
  result.Status = false;
  return result;
 }
}