Odd error with HTML content and attributes disappearing

I have an odd error with an ASP.NET web page (ASP.NET 2.0, C#). For several users at one customer location, on one part of one page, HTML content and attributes are being stripped out. So, something that should look like this:

<p class="adminmainlink">
  <a href="ad_resourcewizard.aspx">Add or edit resources</a>
  <script type="text/javascript">
    var hb526 = new HelpBalloon(
        {
            title: '', 
            content: 'Add or edit downloadable file, web links, and text resources associated with a course.'
        }
    );
  </script>
</p>

In the users' source code looks like this:

<p><a></a><script></script></p>

Not only is the content of the HTML tags disappearing, but also the attributes of the tags (the "class" value for the "p" tag, the "href" from the "a" tag).

Other areas of the same page are being rendered fine, with no changes to the HTML. The HTML isn't being generated by a code-behind page -- it's just plain text in the .aspx page. The area that is rendering correctly is in the .master page; the problem area is inside an asp:Content tag.

This error is only happening on one page of the application. Other, very similar pages that use the same .master page are unaffected. I am not able to reproduce this error outsi开发者_运维百科de of the client's facility, even when logging in to the client's account. The client is using IE 6 -- we have tested on that, and all is OK. No other customers are reporting a similar problem.

Maybe it's a content blocker or firewall issue at the client's location? Maybe the script is causing the content filtering (other pages use the same script and they display fine, however)?

If it's a code problem, it would seem to affect only the area inside the asp:Content control that is dropping into the .master page. Has anyone seen something like this before? What part of the ASP.NET page life cycle would eliminate attributes and tag content from hard-coded HTML? I could see weirdness happening with a control, but with regular HTML?

Many thanks for your thoughts and opinions!

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Are the users using Firefox with AdBlock or some other ad blocking software? I've had strange behaviors in our internal application where certain content was being mysteriously removed, and it turned out it was because a liberal filter was applied, blocking out the word "ad." I noticed "ad_resourcewizard.aspx" was contained in your link. You should have the customers at that location try a different browser or disable their ad blocking software in case it's hooked into their networking software (a plugin for their security suite, for example).

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Check whether they have any internet security software installed, and if so, try disabling it.

I know we had an issue with one of the versions of Norton Internet Security, which was stripping scripts out of our CMS pages for one particular client.