I create a web control such as this:
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="Sys_MObject_Criteria.ascx.cs" Inherits="CDS.Sys.Sys_MObject_Criteria" %>
<%@ Register assembly="Coolite.Ext.Web" namespace="Coolite.Ext.Web" tagprefix="ext" %>
<%@ Register src="Sys_MObject_Windows.ascx" tagname="Sys_MObject_Windows" tagprefix="uc2" %>


<table id="tab_Criteria" runat="server">
<tr>
    <td style="width:30%"  align="left">
    <ext:Label Text="txtObjectID"  runat="Server"></ext:Label>
    </td>
    <td style="width:30%"  align="left">
        <ext:TextField ID="txtObjectID" runat="Server" StyleSpec="width:100%"/>
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label Text="txtObjectName"  runat="Server"></ext:Label></td>
    <td style="width:50%"  align="left">
        <ext:TextField ID="txtObjectName" runat="Server"  StyleSpec="width:100%" />
    </td>
</tr>
<tr>
    <td style="width:30%" align="left"><ext:Label Text="txtObjectText"  runat="Server"></ext:Label></td>
    <td style="width:50%">
        <ext:TextField ID="txtObjectText" runat="Server"  StyleSpec="width:100%"/>
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label Text="ObjectType"  runat="Server"></ext:Label></td>
    <td style="width:50%">
    <ext:ComboBox ID="CmbObjectType" runat="Server"  Width="300"></ext:ComboBox>
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label Text="RefImgPath"  runat="Server" /></td>
    <td style="width:50%">
        <ext:TextField ID="txtRefImgPath"  StyleSpec="width:100%" runat="Server" />
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label ID="Label1" Text="RefEntityPath"  runat="Server" /></td>
    <td style="width:50%">
       <ext:TextField ID="txtRefEntityPath"  StyleSpec="width:100%" runat="Server" />
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label ID="Label2" Text="ParentGuid"  runat="Server" /></td>
    <td style="width:50%">
        <%--<ext:TriggerField ID="txtParentGuid" runat="Server" Width="300">
            <Triggers>
                <ext:FieldTrigger Icon=Combo />
            </Triggers>
            <AjaxEvents>
                <TriggerClick OnEvent="ParentGuid_Search_Click">
                </TriggerClick>
            </AjaxEvents>
        </ext:TriggerField>--%>
        <ext:TriggerField ID="SSS" runat="server" Width="300"></ext:TriggerField>
    </td>
</tr>
<tr>
    <td style="width:30%"  align="left"><ext:Label ID="Label3" Text="MenuIndex"  runat="Server"/></td>
    <td style="width:50%">
       <ext:NumberField ID="numbMenuIndex"  StyleSpec="width:100%" runat="server"/>
    </td>
</tr>
</table>
 <ext:Window ID="Window2"  runat="server" AutoShow="false" Resizable="false" StyleSpec="text-align:center;font-size:16;" Width="430" Height="337" ButtonAlign="Center" Show&#111;nload="false" Modal="true">
    <Body>
        <uc2:Sys_MObject_Windows ID="Sys_MObject_Windows1" runat="server" />
    </Body>
    <Buttons>
            <ext:Button ID="btn_OK" Text="OK" runat="Server">
            <AjaxEvents>
                    <Click OnEvent="btn_OK_Click_Event">
                    </Click>
                </AjaxEvents>
            </ext:Button>
            <ext:Button ID="btn_Exit" Text="Cancel" runat="Server">
            <AjaxEvents>
                <Click OnEvent="btn_Exit_Click_Event">
                </Click>
                </AjaxEvents>
            </ext:Button>
        </Buttons>
    </ext:Window>
I use this control to one aspx page. when i show this page, it occur an error:The system can't find the referred resource. when i use two combobox in one control page , I get the same result. why?