Hello Jeff,

thank you for  fast response, but your suggestions did not help. I tested the cuteditor before and that was working fine.

Page EnableEventValidation="false" ValidateRequest="false" Title="" Language="vb" AutoEventWireup="false" MasterPageFile="~/content.Master" CodeBehind="content_add.aspx.vb" Inherits="zutzu.content_add" 

As soon i delete the editor:

<RTE:Editor id="cedi" Text="" runat="server" EditorBodyClass="../../css/site.css" Width="100%" Height="500" AutoFocus="True" /> 

it works again!