无法使用集合初始化值初始化类型未实现“System.Collections.IEnumerable”

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;namespace WindowsPhoneApplication2.ViewModels
{
    public class CourseTimetableViewModel : INotifyPropertyChanged
    {        public event PropertyChangedEventHandler PropertyChanged;       private  ObservavleCollection<CourseTimetableColumnViewModel> Columns
        {
            get;
              set;
        }
        
        private int _selectedColumnIndex;
        public int SelectedColumnIndex
        {
            get { return _selectedColumnIndex; }
            set
            {
                _selectedColumnIndex = value;
                OnPropertyChanged("SelectedColumnIndex");
            }
        }        private void OnPropertyChanged(string p)
        {
            throw new NotImplementedException();
        }
        public CourseTimetableViewModel()
        {
            Columns = new ObservavleCollection<CourseTimetableColumnViewModel>// 错误地方！！！！！！
            {
                new CourseTimetableColumnViewModel("星期日"),
                new CourseTimetableColumnViewModel("星期一"),
                new CourseTimetableColumnViewModel("星期二"),
                new CourseTimetableColumnViewModel("星期三"),
                new CourseTimetableColumnViewModel("星期四"),
                new CourseTimetableColumnViewModel("星期五"),
                new CourseTimetableColumnViewModel("星期六"),
                
            };
            SelectedColumnIndex=(int)DateTime.Today.DayOfWeek;
        }
    }
}
错误提示为错误 2 无法使用集合初始值初始化类型“WindowsPhoneApplication2.ViewModels.ObservavleCollection<WindowsPhoneApplication2.ViewModels.CourseTimetableColumnViewModel>”，原因是它未实现“System.Collections.IEnumerable” C:\Users\Xuan\Documents\Expression\Blend 4\Projects\WindowsPhoneApplication2\WindowsPhoneApplication2\ViewModels\CourseTimetableViewModel.cs 44 13 WindowsPhoneApplication2
求老大们给看看啊！！急