how to solve this error

Hi i am used two auto completed textbox on autocompletedtextbox selected item based bind another autocompletedtextbox so i try below code here i get one error Microsoft JScript runtime error: 'null' is null or not an object how to solve this

<script src="../jquery-1.5.min.js"type="text/javascript"></script>
<script type="text/javascript">
function Selectarea(source, eventArgs)
{

    $find('Searchautocomplete').set_contextKey(eventArgs.get_value()); 
    
}

</script>
<table>
<tr>
<td>
<asp:TextBox ID="txt_city" runat="server"></asp:TextBox>
<asp:TextBoxWatermarkExtender ID="watermark1" runat="server" TargetControlID="txt_city" WatermarkText="Coimbatore"></asp:TextBoxWatermarkExtender>
<asp:AutoCompleteExtender ID="cityautocomplete" 
TargetControlID="txt_city"
 runat="server" 
  MinimumPrefixLength="1" 
    CompletionInterval="10"
    EnableCaching="true"
    ServiceMethod="GetCompletionList"
    OnClientItemSelected="Selectarea" 
 ServicePath="~/AutoComplete.asmx"></asp:AutoCompleteExtender>
</td>
<td>
<asp:TextBox ID="txt_Search" runat="server" Height="21px" Width="281px"></asp:TextBox>
<asp:AutoCompleteExtender ID="Searchautocomplete"  
TargetControlID="txt_Search"
 runat="server" 
  MinimumPrefixLength="1" 
    CompletionInterval="10"
    EnableCaching="true"
    ServiceMethod="GetSearchList"
 ServicePath="~/AutoComplete.asmx"></asp:AutoCompleteExtender>
<asp:TextBoxWatermarkExtender ID="TextBoxWatermarkExtender1" runat="server" TargetControlID="txt_Search" WatermarkText="Search Example - ICICI Bank"></asp:TextBoxWatermarkExtender>

</td>
<td>
<asp:TextBox ID="txt_Place" runat="server"> </asp:TextBox>
<asp:AutoCompleteExtender ID="AutoCompleteExtender1" 
TargetControlID="txt_Place"
 runat="server" 
  MinimumPrefixLength="1" 
    CompletionInterval="10"
    EnableCaching="true"
    ServiceMethod="GetAreaList"
 ServicePath="~/AutoComplete.asmx"></asp:AutoCompleteExtender>
<asp:TextBoxWatermarkExtender ID="TextBoxWatermarkExtender2" runat="server" TargetControlID="txt_Place" WatermarkText="Rspuram"></asp:TextBoxWatermarkExtender>

</td>
<td>
<asp:Button ID="btn_Search" runat="server" Text="Go" onclick="btn_Search_Click" />
</td>
</tr>

</table>

gowthaman8870226416