SendMessage {ENTER} to Internet Explorer browser iFrame element - vb.net

Question

I have a little project that needs me to automate IE.
I've used SHDocVw.InternetExplorer class for the initial move. (attaching to IE)
But after that I want to use the Windows API to get focus to browser element and to click it.
I know that I can do this job more easy with the built in function of SHDocVw.InternetExplorer, or use 3rd party class like Watin
But this time I want to use Windows API.
This is work perfect when I open IE browser and find some links/element to click
I used the key press {TAB} to iterate thru HTML elements then read the IE status bar to get its link. Then I use the key press {ENTER} to click/execute it.
I got problem when the element that are selected by {TAB} are inside iFrame, the keypress {ENTER} not work.
Here is my sample code
Imports WindowsApplication1.win_Api
Module browser
Public Class IE
Private Shared IE As SHDocVw.InternetExplorer
Sub New(Optional ByVal url As String = "about:blank")
Dim bw As New SHDocVw.InternetExplorer
IE = bw
Try
IE.Navigate(url)
Catch ex As Exception
End Try
End Sub
Shared Sub click(byval url as string)
Dim Z As Integer = 0
Do While Z = 0
IE.Stop()
'Send keboard press TAB this API is work perfect
SendMessage(IE.HWND, WM_IME_KEYDOWN, Keys.Tab, 0)
IE.Stop()
If IE.StatusText = url Then
Z = 1
End If
Loop
For Each I As IntPtr In GetChildWindows(IE.HWND)
Dim L As Integer = 256
Dim sb As New System.Text.StringBuilder(L)
GetClassName(I, sb, L)
If sb.ToString = "Internet Explorer_Server" Then
'Send keyboard press ENTER, this work
'But not work if the element selected by TAB action is on iframe
SendMessage(I, WM_CHAR, Keys.Enter, 0)
End If
Next
End Sub
End Class
End Module