I have one navigationmenu on my masterpage. Whenever a user logins, the navigationmenu should display the menuitems as per the users permission.

eg: i have three navigationmenu items i.e. menuitem1, menuitem2, menuitem3.
a normal user has access only to two menuitems i.e. menuitem1 and menuitem2. And the third menuitems is either disable or hidden to him.

So when a user logins, he can only see two menuitems i.e. menuitem1 and menuitem2.
My Program: wht I did is I wrote user authentication code on my login.aspx page

If lbl.Text = "user" Then
end if

HERE nwperm is a function which i wrote in the class file located in App_Code folder.

Sub nwperm()

Dim mymenu As Menu = Master.FindControl("NavigationMenu")

Dim mymi As MenuItem = mymenu.FindItem("TechnicalSupport")

mymi.Enabled =True

end sub

Problem/error: object reference cannot create an instance of an object.
Plz help me...