cannot fill dropdownlist when Formview is in insert or edit template

Gents,
I have formview and around 10 dropdown lists when I place them into itemtemplate its populated fine but when I tried to add new record
or edit existing one it’s give me :Object reference not set to an instance of an object..
This is my code snippet:
 
 
 
<asp:FormView ID="Fmv_TeacherPage" runat="server" CssClass="style1" OnItemCommand="Fmv_TeacherPage_OnItemCommand"> <ItemTemplate> <table id="tbl_ItemTemplate"> <tr> <td> TeacherName </td> <td> <asp:Label ID="ItemTemplate_lbl_TeacherName" Text='<%# Eval("TeacherName") %>' runat="server"></asp:Label> </td> </tr> <asp:LinkButton ID="lnkNew" Text="New" CommandName="ItemTemplate_New" runat="server" /> |<asp:LinkButton ID="lnkEdit" Text="Edit" CommandName="ItemTemplate_Edit" CausesValidation="false" runat="server" /> |<a ...