tab key in modalles form

i write a dll in c# which show a modalless form. tab key didn't work in the form. I red the article "How to Make TAB Key Work in Modeless Winforms" in
http://newsletter.plmworld.org/archive/Vol6No4/nx_TAB_key.php
and I used that. now my tab key works but when I press a key its character type 4 times in textbox.
Could any one help me?
regards