Value '0' não é um valor válido para 'SelectedIndex'.

System.ArgumentOutOfRangeException was unhandled
  HResult=-2146233086
  Message=InvalidArgument=Value '0' não é um valor válido para 'SelectedIndex'.
Nome do parâmetro: SelectedIndex
  Source=System.Windows.Forms
  ParamName=SelectedIndex
  StackTrace:
       em System.Windows.Forms.ComboBox.set_SelectedIndex(Int32 value)
       em RemoteConsole.MainForm.AddMailTypeList(List`1 typeList) na D:\zhyz\Server Source\RemoteConsole\RemoteConsole\MainForm.cs:linha 124
       em RemoteConsole.Program.Main() na D:\zhyz\Server Source\RemoteConsole\RemoteConsole\Program.cs:linha 74
       em System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       em System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       em Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       em System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       em System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       em System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       em System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       em System.Threading.ThreadHelper.ThreadStart()
  InnerException:


Code:        public void AddMailTypeList(List<MailTypeCfg> typeList)
        {
            foreach (MailTypeCfg ty in typeList)
            {
                comboBox2.Items.Add(ty.desc);
            }
            comboBox2.BeginUpdate();
            comboBox2.SelectedIndex = 0;
            comboBox2.EndUpdate();
        }

Help Pls!