The code of my ASPX follows.
However, I added a new project, and re-added all my ASPX pages to the new project and the two-editor problem disappeared. And yes, I removed all the previous cute editor client files and dll files etc. Thanks.
<%@ Page language="c#" Codebehind="am_AddText.aspx.cs" AutoEventWireup="false" Inherits="evis.CMSUIL.admin.maint.am_AddText1" %>
<%@ Register TagPrefix="CE" Namespace="CuteEditor" Assembly="CuteEditor" %>
<HTML>
<HEAD></HEAD>
<body>
<form runat="server" ID="Form1" target="AddTextWindow" >
<table border="0" cellpadding="0" cellspacing="0">
<tr>
<td valign="top" width="760"><STRONG>CMS</STRONG>
<hr>
ECV - CMS New CuteEditor Test
<br>
<br>
<CE:Editor id="Editor1" Height="200" runat="server" TemplateItemList="Bold,Italic,Underline,JustifyLeft,JustifyCenter,JustifyRight,InsertUnorderedList,Separator,Indent, Outdent, insertcustombutonhere, netspell, Separator, paste, CssClass,InsertAnchor"></CE:Editor>
</td>
<tr>
<td id="tdComplete">
<asp:Label id="lblComplete" runat="server"></asp:Label></td>
</tr>
<tr>
<td>
<asp:ImageButton id="ibtnSubmit" runat="server"></asp:ImageButton></td>
</tr>
</table>
</form> </body>
</HTML>