Object reference not set to an instance of an object.

Hai ,
I'm Using Ajax Auto Complete Control using Sql server
my code is:
aspx:
 <table>             <tr>                 <td>                     <asp:Label ID="lbllStateName" runat="server" Text="StateName"></asp:Label>                 </td>                 <td>                     <asp:TextBox runat="server" ID="txtStateName"></asp:TextBox>   ...