I decided to have a shadow with my form so I used this property in my form:
Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
Dim cp As System.Windows.Forms.CreateParams = MyBase.CreateParams
cp.ClassStyle = cp.ClassStyle Or &H20000
It is working perfectly if I open my form using ".show()"
But if I open the form as a modal dialog box using ".showDialog(owner)", the shadow (over the owner form) disapear if I move the form or if the form lose focus.
Does someone know how to solve this problem?