Common Dialog Problem

I use the Common Print Dlg and modifying it.. adding more control and it work. allmost..
but in the PrintDialog i now have a button for selection a file. and when pressing it, it should open the common fileopen dialog.. BUT it don't work. it dont open it. if I alt+tab away from my app. and then alt+tab back and press the button.. it opens the 'openfile dialog'. but when it closes and i press it again it wont open again.. Anyone had this problem. anyone have a solution.. ??