>>With the breakpoint set on this line, I pressed F5. IE opened and displayed the page with the caption on button1 changed to "Test" - yet the program did not stop at the breakpoint. This is a weird one.
>
>Yep. Do you get see the same behavoir if you create a brand new Web Application? Do you have anything suspect in your web.config file?

I was just about to post an update. I found the resolution here:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q306169&SD=MSKB&

Al