Error SendInput on 64-bit

Question

Possible duplicate:
SendInput and 64bit

I am using SendInput from .NET code (PInvoke). The code used to work on a 32-bit OS, but now on WIN7 SendInput returns 0, and the last error is set to 57 (ERROR_INVALID_PARAMETER).
I can not compile my code as x86, since I boot to a 64-bit host. In addition, I tried various solutions regarding the size of the structure and the field offsets, no one worked.
These are my imports and PInvoke types:

[StructLayout(LayoutKind.Sequential)]
struct KEYBOARD_INPUT
{
    public uint type;
    public ushort vk;
    public ushort scanCode;
    public uint flags;
    public uint time;
    public uint extrainfo;
    public uint padding1;
    public uint padding2;
}

[DllImport("User32.dll", SetLastError=true)]
private static extern uint SendInput(
    uint numberOfInputs, 
   [MarshalAs(UnmanagedType.LPArray, SizeConst = 1)] KEYBOARD_INPUT[] input,
   int structSize);

and code usage:

uint result = SendInput(
       (uint)inputs.Count, 
       inputs.ToArray(), 
       Marshal.SizeOf(inputs[0]));

where the input array contains 1 KEYBOARD_INPUT struct.
this gives the result = 0, and when I check the last error, I get that the last error is set to 57 (ERROR_INVALID_PARAMETER, the parameter is incorrect).

64- 64- WIN7? XP...

Answer 1

( pinvoke.net):

const int INPUT_MOUSE = 0;
const int INPUT_KEYBOARD = 1;
const int INPUT_HARDWARE = 2;
const uint KEYEVENTF_EXTENDEDKEY = 0x0001;
const uint KEYEVENTF_KEYUP = 0x0002;
const uint KEYEVENTF_UNICODE = 0x0004;
const uint KEYEVENTF_SCANCODE = 0x0008;

struct INPUT
{
    public int type;
    public InputUnion u;
}

[StructLayout(LayoutKind.Explicit)]
struct InputUnion
{
    [FieldOffset(0)]
    public MOUSEINPUT mi;
    [FieldOffset(0)]
    public KEYBDINPUT ki;
    [FieldOffset(0)]
    public HARDWAREINPUT hi;
}

[StructLayout(LayoutKind.Sequential)]
struct MOUSEINPUT
{
    public int dx;
    public int dy;
    public uint mouseData;
    public uint dwFlags;
    public uint time;
    public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
struct KEYBDINPUT
{
    /*Virtual Key code.  Must be from 1-254.  If the dwFlags member specifies KEYEVENTF_UNICODE, wVk must be 0.*/
    public ushort wVk;
    /*A hardware scan code for the key. If dwFlags specifies KEYEVENTF_UNICODE, wScan specifies a Unicode character which is to be sent to the foreground application.*/
    public ushort wScan;
    /*Specifies various aspects of a keystroke.  See the KEYEVENTF_ constants for more information.*/
    public uint dwFlags;
    /*The time stamp for the event, in milliseconds. If this parameter is zero, the system will provide its own time stamp.*/
    public uint time;
    /*An additional value associated with the keystroke. Use the GetMessageExtraInfo function to obtain this information.*/
    public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
struct HARDWAREINPUT
{
    public uint uMsg;
    public ushort wParamL;
    public ushort wParamH;
}

[DllImport("user32.dll")]
static extern IntPtr GetMessageExtraInfo();

[DllImport("user32.dll", SetLastError = true)]
static extern uint SendInput(uint nInputs, INPUT[] pInputs, int cbSize);

:

INPUT[] inputs = new INPUT[]
{
    new INPUT
    {
        type = INPUT_KEYBOARD,
        u = new InputUnion
        {
            ki = new KEYBDINPUT
            {
                wVk = key,
                wScan = 0,
                dwFlags = 0,
                dwExtraInfo = GetMessageExtraInfo(),
            }
        }
    }
};

SendInput((uint)inputs.Length, inputs, Marshal.SizeOf(typeof(INPUT)));