OnSelectedIndexChanged DDL not working now in .NET2. WebResource.axd culprit?

(repost!)

I have a simple and common scenario. I'm developing pages in VWD and FTP-ing
them over to a test servr running Window 2003, NET2 Framework. On my page,
I have a DDL that causes a postback and executes a sub when the value has
changed. For some reason, it just quit working. I get a js error in IE6
(but NOT in FF 1.5) and gives me a vague error about:

'event' is null or not an object.Line X, character X.

I try to find line X in my markup (view source) and it's nothing even close
to the right line. I whip up a new test page and have a DDL change a
label's text with OnSelectedIndexChanged and all works fine. Yet, my page
that has worked for months just "stopped" working. I added a new DDL to
the same page and called the same sub and got the same error.

After doing some searching, I found this thread where this guy had the same
problem: http://forums.asp.net/thread/1146679.aspx

However, I don't really understand his workaround or the Project Conversion
Wizard (huh?) solution from MS. I never converted this page from 1.1 to
2.0. It has always been a 2.0 page created in VWD Express. After comparing
the source code from my whipped up test page and my now failing page, I
found this line in my failing page and it is NOT in my test page:

<script
src="/olga3/WebResource.axd?d=0SzioPWWyjhw2E9CY1GR8w2&amp;t=63 2749912169396975"
type="text/javascript"></script>

I looked and all of my pages in my .NET app have this line in browser source
code. Yet, any NEW pages I create in this app don't show this in my source
code on the test server.

What is this line and why is it there? There is no WebResource.axd file on
my test server. Could this be the problem? How did this happen? I
recently did a massive Windows update - was the .NET2 framework recently and
quietly updated causing this? What is my solution?

I have uninstalled NET2 on the server and completely reinstalled it. I also
deleted all files on the server and put fresh copies on it. Problem still
occurs.

Thanks in advance for all help!!

Groove