DateTimePicker via SendMessage

[Sweetve13]

I am wanting to get and change the display date in the datetimepicker control located in a 3rd party application that runs in the background and thus not in focus. I found that DTM_GetSystemTime and DTM_SetSystemTime can do this but I have been unable to get it to work. I get an error message stating:

"A call to PInvoke function 'DateTimePicker!DateTimePicker.Form1::SendMessage' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature."

On a side note, I can get and set the SystemTray timeclock via GetSystemTime and SetSystemTime. This assures me that the SystemTime structure should be ok (works with short/int16). Any suggestions? Thanks.

Imports System.Runtime.InteropServices

    Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As Int32) As Int32
    Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As SYSTEMTIME) As Int32
    Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As String) As Int32
    Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Int32
    Declare Function FindWindowEx Lib "user32.dll" Alias "FindWindowExA" (ByVal hWnd1 As Int32, ByVal hWnd2 As Int32, ByVal lpsz1 As String, ByVal lpsz2 As String) As Int32

    Const DTM_FIRST As Int32 = &H1000
    Const DTM_GETSYSTEMTIME As Int32 = (DTM_FIRST + 1)
    Const DTM_SETSYSTEMTIME As Int32 = (DTM_FIRST + 2)

    <StructLayout(LayoutKind.Sequential)> Structure SYSTEMTIME
        Public wYear As Int16
        Public wMonth As Int16
        Public wDayOfWeek As Int16
        Public wDay As Int16
        Public wHour As Int16
        Public wMinute As Int16
        Public wSecond As Int16
        Public wMilliseconds As Int16
    End Structure

        Dim hwnd, datehwnd, txtboxhwnd As Integer
        Dim gettime As New SYSTEMTIME
        Dim changetime As New SYSTEMTIME
        changetime.wDay = 22
        changetime.wMonth = 10
        changetime.wYear = 2005

        hwnd = FindWindow(vbNullString, "Application_Name")
        datehwnd = FindWindowEx(hwnd, 0, "DateTimePickerClassInfo", vbNullString)

        SendMessage(datehwnd, DTM_GETSYSTEMTIME, 0, gettime)
        SendMessage(datehwnd, DTM_SETSYSTEMTIME, 0, changetime)

    End Sub