Ссылка на объект не указывает на экземпляр объекта в модели представления

Я получаю эту ошибку:

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error: 
Line 251:            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);
Line 252:
Line 253:            Currencies = new SelectList(
Line 254:            ManageCurrency.Instance.getCurrencies(), "id", "name",_Account.currency1.id);
Line 255:

Это дает ошибку в этой модели представления

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;
using Common;
using Business;
using System.Web.Mvc;
using System.Web.Security;
using System.Runtime.Remoting.Contexts;

namespace internetBankingApplication.ViewModel
{

    public class NewFixedAccountViewModel
    {
        private account _Account { get; set; }

        private fixedAccount _FixedAccount { get; set; }



        public SelectList AccountTypes { get; set; }

        public SelectList Durations { get; set; }

        public SelectList AccountFromList { get; set; }

        public SelectList Currencies { get; set; }

        public int ID
        {
            get
            {
                return _Account.accountID;
            }
        }

        [Required]
        [Display(Name = "Account Name")]
        public string Name
        {
            get
            {
                return _Account.name;
            }
            set
            {
                _Account.name = value;
            }
        }

        [Required]
        [Display(Name = "Account From")]
        public int accountFrom { get;set;}



        public string AccountFromName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageAccount.Instance.GetAccountBYID(accountFrom).name;
                }
                catch { }
                return result;
            }
        }



        [Required]
        [Display(Name = "Duration")]
        public int duration
        {
            get
            {
                return _FixedAccount.duration;
            }
            set
            {
                _FixedAccount.duration = value;
            }
        }

        public string durationName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageDuration.Instance.GetDurationById(_FixedAccount.duration).duration1;
                }
                catch { }
                return result;
            }
        }

        [Required]
        [Display(Name = "Available Balance")]
        public decimal AvailableBalance
        {
            get
            {
                return _Account.availableBalance;
            }
            set
            {
                _Account.availableBalance = value;
            }
        }

        [Required]
        [Display(Name = "Currency")]
        public int currency
        {
            get
            {
                return _Account.currency;
            }
            set
            {
                _Account.currency = value;
            }
        }

        public string CurrencyName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageCurrency.Instance.getTypesByID(_Account.currency).name;
                }
                catch { }
                return result;
            }
        }


        [Required]
        [Display(Name = "Account Description")]
        public string Description
        {
            get
            {
                return _Account.description;
            }
            set
            {
                _Account.description = value;
            }
        }


        [Required]
        [Display(Name = "Account Renew")]
        public bool renew
        {
            get
            {
                if (_FixedAccount.renew == 0)
                {
                    return false;
                }
                return true;
            }
            set
            {
                if (value == false)
                {
                    _FixedAccount.renew = 0;
                }
                else
                {

                    _FixedAccount.renew = 1;
                }
            }
        }


        public NewFixedAccountViewModel()
        {
           // AccountTypes = new SelectList(
           //ManageAccountType.Instance.getTypes(), "id", "type", _Account.typeID);

            string username = HttpContext.Current.User.Identity.Name.ToString();
            AccountFromList = new SelectList(
            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);

            **Currencies = new SelectList(
            ManageCurrency.Instance.getCurrencies(), "id", "name",_Account.currency1.id);** //Giving the error

            Durations = new SelectList(
            ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);



        }

        public NewFixedAccountViewModel(string username)
        {
            AccountTypes = new SelectList(
            ManageAccountType.Instance.getTypes(), "id", "type", _Account.typeID);


            AccountFromList = new SelectList(
            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);

            Currencies = new SelectList(
            ManageCurrency.Instance.getCurrencies(), "id", "name", _Account.currency);

            Durations = new SelectList(
            ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);


        }

        public NewFixedAccountViewModel(int accountID, string username)
        {
            _Account = ManageAccount.Instance.GetAccountBYID(accountID);

            _FixedAccount = ManageFixedAccount.Instance.GetFixedAccountByID(accountID);

            AccountFromList = new SelectList(
            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);

            AccountTypes = new SelectList(
            ManageAccountType.Instance.getTypes(), "id", "type", _Account.accountType);

            Currencies = new SelectList(
            ManageCurrency.Instance.getCurrencies(), "id", "name", _Account.currency);

            Durations = new SelectList(
            ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);


        }
    }
}