I dono if you pasted the whole code or not for the aspx.. but if this is the whole code all the closing tags are missing.
<asp:DropDownList ID="Search_query1" CssClass="search_drdown" Width="162px" runat="server">
<asp:ListItem Value="BRANCH.SHORTNAME">Short Name
<asp:ListItem Value="BRANCH.LONGNAME">Long Name
<asp:ListItem Value="BRANCH.CONTACT_PERSON1">Contact Person 1
Change the aspx to this. and try if the error persists.
Regards,
Ibrahim Karakira