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

[Hung]

Hi support team,
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,

Most probably the issue you encountered is Web Resources related. Please check the help article Web Resources Troubleshooting for more information on troubleshooting the web resource that loads the RadCaptcha image. You can also check if the problem persists when the captcha's skins and scripts are loaded via the Telerik CDN.

If the you are still having difficulties, please open a support ticket and send a simple, runnable page that isolates your case so that I can inspect it locally and provide an according solution.

All the best,
Slav
the Telerik team

[Hung]

Hi Slav,

Thanks for your info, but I tried all in Web Resources Troubleshooting link but the issue persist.
I could not provide you a link which occurs the issue. b/c it is on the server'client and not published.
All configuration as I provided you in previous thread.
I can not re-produce it on my local, b/c it is different environment.
Our client server's configuration:

1. Moss 2007
2. Reverse Proxy, 
3. Https

But I wonder that why the third time the error script occur instead of 1st or 2nd time.
I highly appreciate if you could help me sort out the issue.
Many thanks.

[Slav]

Hello Hung,

The behavior you described is quite strange and it was not reported before. Could you please inspect the traffic between your client and the server via Fiddler and send us the logs as this information could be useful for inspecting the cause of the problem?

Also, in your code sample I noticed only the <system.web> configuration section. Note that if the web site is running under IIS7 Integrated mode the web server searches the HttpHandler registrations under the <system.webServer> configuration section. This help article displays the full code for configuring the HttpHandler.

As described in help article, linked above, you need to setup an out of process Session State when the captcha is used in a load balanced scenario. I would suggest checking if this requirement is fulfilled in your case.

Greetings,
Slav
the Telerik team

[Hung]

Hi Slav,
Finally, I overcome it.
The root cause is a rule of url rewriter.
The rule changed to another url which is not existing.