A call to PInvoke function unbalanced the stack.

I got this error when running the following code:
A call to PInvoke function 'tonin_image!tonin_image.Form1::ShellExecute' 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.


Public Class Form1

    Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles a.Click
        Dim HttpJump
        Dim MyUrl As String

        MyUrl = "http://server/default.aspx?lease=" + a.Text + "&file_sufx=" + File_Sufx.Text
        ShellExecute(0, "", MyUrl, "", "", vbNormalFocus)

    End Sub
End Class