c# programatically selecting dropdown value

I am new at C# and it seems the following code below does not seem to select my combobox value:

Code:

---

    private void button1_Click(object sender, EventArgs e)
    {
      cbPortNumber.SelectedIndex = 3;
    }

---

The dropdown looks like this:
http://i.stack.imgur.com/JP7FR.jpg

All code above does not seem to select HDMI 4 on the list... The error i have is:

System.ArgumentOutOfRangeException: InvalidArgument=Value of '2' is not valid for 'SelectedIndex'. Parameter name: SelectedIndex at System.Windows.Forms.ComboBox.set_SelectedIndex(Int32 value)

Any help would be great!

**update showing combobox**
http://i.stack.imgur.com/4dcHs.png

Code:

---

        //
        // cbPortNumber
        //
        this.cbPortNumber.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.Append;
        this.cbPortNumber.Enabled = false;
        this.cbPortNumber.FormattingEnabled = true;
        this.cbPortNumber.Location = new System.Drawing.Point(174, 40);
        this.cbPortNumber.Name = "cbPortNumber";
        this.cbPortNumber.Size = new System.Drawing.Size(133, 21);
        this.cbPortNumber.TabIndex = 11;
        this.cbPortNumber.Text = "global_hdmi_port";
        this.helpPortNumber.SetToolTip(this.cbPortNumber, "The HDMI port number, to which you connected your USB-CEC adapter.");
        this.cbPortNumber.SelectedIndexChanged += new System.EventHandler(this.cbPortNumber_SelectedIndexChanged);

---

Code:

---

    #region Global settings
    public CECSettingByte HDMIPort
    {
      get
      {
        if (!_settings.ContainsKey(KeyHDMIPort))
        {
          CECSettingByte setting = new CECSettingByte(KeyHDMIPort, "HDMI port", 1, _changedHandler) { LowerLimit = 1, UpperLimit = 15, EnableSetting = EnableHDMIPortSetting };
          setting.Format += delegate(object sender, ListControlConvertEventArgs args)
          {
            ushort tmp;
            if (ushort.TryParse((string)args.Value, out tmp))
              args.Value = "HDMI " + args.Value;
          };

          Load(setting);
          _settings[KeyHDMIPort] = setting;
        }
        return _settings[KeyHDMIPort].AsSettingByte;
      }
    }

---

And this is what fires the action after selecting something in that dropdown:

Code:

---

    private void OnSettingChanged(CECSetting setting, object oldValue, object newValue)
    {
      if (setting.KeyName == CECSettings.KeyHDMIPort)
      {
        CECSettingByte byteSetting = setting as CECSettingByte;
        if (byteSetting != null)
        {
          if (!Settings.OverridePhysicalAddress.Value)
            Config.HDMIPort = byteSetting.Value;
          CECActions.SetConnectedDevice(Settings.ConnectedDevice.Value, byteSetting.Value);
        }
      }

---

Quote:

---

System.ArgumentOutOfRangeException: InvalidArgument=Value of '2' is not valid for 'SelectedIndex'. Parameter name: SelectedIndex at System.Windows.Forms.ComboBox.set_SelectedIndex(Int32 value)

---

This error means that, the specified SelectedIndex is equal to or greater than the combobox items count.

Code:

---

InvalidArgument=Value of '2' is not valid for 'SelectedIndex'.

---

You don't have enough items to have an index of 2, as it's out of range, as the user above mentioned. So you probably don't have all of those values at the time you are changing the selectedindex.