directcast giving exception while trying to findcontrol in content page...

Hi,
im using master-content page for designing one web page. in which i need to make some control visible at run time using codebehind. for that im using directcast function to find out the control and make it visible. me gettiing problem while using it. it always gives object reference not set to an instance exception althought control exist there in content page.


here is my aspx page: (code is from content page not from master page)

<input id="txtItemLocation" runat="server" name="txtItemLocation" type="text" value="Where in Mumbai?" />
                                        <asp:ImageButton ID="imgAddLocation" runat="server" ImageUrl="Images/add.JPG" / ...