If i send a WM_CLOSE message my program freezes

[IronRazer]

I am working on a program that sends keys, button clicks, and so on to external windows. If i send a close command to notepad or wordpad and it pops up the (save file dialog window) it freezes my program. I can`t even click on my program window to bring it back into focus until i click yes, no, or cancel on the (save file dialog window). This stops my program from finding the dialog window so i can send it a button click. Why is it freezing my program ?

This is an example of my code:

    Private Sub TSB_Close_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TSB_Close.Click
        SendMessage(hWnd, WM_CLOSE, 0, 0)

        'It seems to freeze here if a popup Dlg window is created by the
        'program that is recieving the close message. If no popup Dlg
        'window is created then it continues with no problems.

        CheckForPopupDlgWindow(LB_Id.SelectedItem.ToString)
    End Sub

    Private Sub CheckForPopupDlgWindow(ByVal parentID As String)
        'This is the Class of the popup dialog window to find
        Dim popupDlgclass As String = "#32770"

        'Get desktop handle
        Dim hWnddesktop As IntPtr = IntPtr.Zero
        hWnddesktop = GetDesktopWindow()

        'Find the first desktop child window with the same class as (popupclass)
        Dim popuphandle As IntPtr = IntPtr.Zero
        popuphandle = FindWindowEx(hWnddesktop, popuphandle, popupDlgclass, IntPtr.Zero)

        'if a (popuphandle) is found with the same class then check if it has same ID as (parentID)
        While (Not popuphandle.Equals(IntPtr.Zero))

            'Get the ID for (popuphandle)
            Dim foundProcID As UInt32 = Nothing
            GetWindowThreadProcessId(popuphandle, foundProcID)

            'If the (popuphandle) has the same ID as the parentID then add it to listbox and stop looking
            If foundProcID.ToString = parentId Then
                LB_DlgPopupWindows.Items.Add(popuphandle.ToString)
                Exit While
            End If

            'Get the next desktop child window to check if one has not been found
            popuphandle = FindWindowEx(hWnddesktop, popuphandle, popupDlgclass, IntPtr.Zero)
        End While
    End Sub

[tlhintoq]

To be picky it doesn't freeze your program - it freezes that thread.
If your program is single threaded then you are fraked.

So you probably need to make it multi-threaded so it can continue to look for these new pop-ups and handle them.