Telerik captcha click Generate New Image link more 3 times get script error.

[Hung]

Hi all,
I get a script error after clicking on Generate New Image link more 3 times.
It means that the first and second time, the image is generated successfully.
But in the third time, there is a script error and image is not generated, refer to scripterror.jpg.
Error detail:
Message: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 404
Line: 6
Char: 62099
Code: 0
URI: http://[My Server]/Telerik.Web.UI.WebResource.axd?_TSM_HiddenField_=ctl00_PlaceHolderMain_ctl00_ctl00_ctl00_RadScriptManager1_TSM&compress=1&_TSM_CombinedScripts_=%3b%3bSystem.Web.Extensions%2c+Version%3d3.5.0.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d31bf3856ad364e35%3aen-US%3a55ab6258-ebc5-40d7-ae7b-b95de6f72668%3aea597d4b%3ab25378d2%3bTelerik.Web.UI%2c+Version%3d2011.3.1115.35%2c+Culture%3dneutral%2c+PublicKeyToken%3d121fae78165ba3d4%3aen-US%3ad841c84c-68bb-4f5c-b77b-50f39a462ac8%3a16e4e7cd%3ab7778d6c%3ae085fe68%3ac08e9f8a%3a1bb784d4%3a11e117d7

My configuration is here:
Browser: IE8
The captcha is integrated into MOSS 2007.
<telerik:RadCaptcha ID="RadCaptchaControl" runat="server" ErrorMessage="The code you entered is not valid."
                        ValidationGroup="captchagroup" ValidatedTextBoxID="txtRadCaptcha" Display="Dynamic"
                        EnableRefreshImage="true" CaptchaImage-EnableCaptchaAudio="true" CaptchaImage-UseAudioFiles="true" ImageStorageLocation="Session"
                        CaptchaImage-AudioFilesPath="_layouts/Audio/RadCaptcha">
                        <CaptchaImage EnableCaptchaAudio="true" RenderImageOnly="true" ImageCssClass="rcCaptchaImage" 
                            BackgroundColor="#609f0a" TextColor="Black" BackgroundNoise="None" ImageAlternativeText="captcha use audio" />
                    </telerik:RadCaptcha>
web.config:
<httpHandlers>
<add path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResourceSession, Telerik.Web.UI, Version=2011.3.1115.35, Culture=neutral, PublicKeyToken=121fae78165ba3d4" verb="*" validate="false" />
</httpHandlers>
The reason I configured type="Telerik.Web.UI.WebResourceSession" b/c there are 2 servers (load balance).  

<handlers>
<add name="Telerik.Web.UI.WebResource" path="Telerik.Web.UI.WebResource.axd" verb="*" type="Telerik.Web.UI.WebResource, Telerik.Web.UI" />
</handlers>

<location path="Telerik.Web.UI.WebResource.axd">

    <system.web>

        <authorization>

            <allow users="*"/>

        </authorization>

    </system.web>

</location>

I used UrlRewriter in my app, but I also apply this article: http://www.iis.net/learn/extensions/url-rewrite-module/url-rewriting-for-aspnet-web-forms 
 <rule name="do not rewrite axd files" stopProcessing="true">
          <match url="\.axd$" />
          <conditions>
            <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
            <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />
          </conditions>
          <action type="None" />
        </rule>
I appreciate if you can help me sort out the problem. Many Thanks. 

[Slav]

Hello Hung,

I addressed your issue in the other forum thread on the matter. Please examine the provided information and check if it will help you resolve the problem.

I would suggest continuing our discussion in the other thread.  The information about your scenario will be easier to track if it is contained in a single thread.

Regards,
Slav
the Telerik team