Michel,

>If someone could suggest things to look for in an attempt to resolve the issue, that would be greatly appreciated.

Perhaps someone else can comment on your global.asax configuration of the framework object -- I don't have enough experience in .NET to do that. It sure sounds like some kind of session mixup.

There have been some documented cross-session mixups due to "kernel-mode output caching" under certain circumstances related to setting cookies -- basically resulting in the SetCookie being cached in the request and attaching other users to the same session via the cached SetCookie.

This might not be at all related to your situation, but it's explained very well by Jeff Prosise in the MSDN Mag July 2006 issue: "Keep Sites Running Smoothly By Avoiding These 10 Common ASP.NET Pitfalls":

http://msdn.microsoft.com/msdnmag/issues/06/07/WebAppFollies/

(Look in the section on Sessions and Output Caching). This is one of the best articles I have seen on asp.net potential performance and session problems.

Good luck on finding the problem.