Send keys through SendInput in user32.dll

I am using this board as a keyboard for demo purposes.

Anyways to make the long story short everything works fine except for very few cases. I send keystrokes with the SendInput function located in user32.dll.

So my program looks like:

static void Main(string[] args)
{
    Console.Write("Press enter an on the next secont the key combination shift+end will be send");
    Console.Read();

    Thread.Sleep(1000);

    SendKeyDown(KeyCode.SHIFT);
    SendKeyPress(KeyCode.END);
    SendKeyUp(KeyCode.SHIFT);

    Console.Read(); 
    Console.Read();
}

[DllImport("user32.dll", SetLastError = true)]
private static extern uint SendInput(uint numberOfInputs, INPUT[] inputs, int sizeOfInputStructure);

/// <summary>
/// simulate key press
/// </summary>
/// <param name="keyCode"></param>
public static void SendKeyPress(KeyCode keyCode)
{
    INPUT input = new INPUT {
        Type = 1
    };
    input.Data.Keyboard = new KEYBDINPUT() {
        Vk = (ushort)keyCode,
        Scan = 0,
        Flags = 0,
        Time = 0,
        ExtraInfo = IntPtr.Zero,
    };

    INPUT input2 = new INPUT {
        Type = 1
    };
    input2.Data.Keyboard = new KEYBDINPUT() {
        Vk = (ushort)keyCode,
        Scan = 0,
        Flags = 2,
        Time = 0,
        ExtraInfo = IntPtr.Zero
    };
    INPUT[] inputs = new INPUT[] { input, input2 };
    if (SendInput(2, inputs, Marshal.SizeOf(typeof(INPUT))) == 0)
        throw new Exception();            
}

/// <summary>
/// Send a key down and hold it down until sendkeyup method is called
/// </summary>
/// <param name="keyCode"></param>
public static void SendKeyDown(KeyCode keyCode)
{
    INPUT