Forms authentication redirect puzzle with ASP.NET 1.1

[Rick]

I'm testing an implementation of forms authentication using VB.NET and
ASP.NET 1.1. Basically I'm using standard MSDN example code to get some
experience.

As I trace the code using Visual Studio on my local machine, I can see that
I successfully validate the password and then execute code to redirect the
page to the proper next page. However, the browser page always returns to
the login page as if the login failed. Sometimes I can hand enter the
address of the target page and get it to work, but sometimes not.

If I move the same code to a web site, the authentication seems to work
properly.

While trying to troubleshoot this, I installed the "Fiddler" HTTP monitor.
With the monitor turned on but otherwise with no changes to my code, the
redirect goes to the proper page in the local debugger and the authentication
appears to work properly.

Is there some system task that has to complete for authentication to work,
and maybe my local machine operates too fast until it is slowed down by
Fiddler monitoring? But that's just a guess.

Any ideas why forms authentication doesn't work in the debugger for me?

Thanks,