aspnet_wp.exe stopped unexpectly error

[Shirley]

I wrote an asp.net page with code that calls a third party ActiveX control.
As that ActiveX control has to run on a thread in Single-threaded Apartment
mode, a thread is started so the ActiveX control can be created and called in
my C# code. My problem is: whenever I make a couple of actions that call the
ActiveX control in my asp.net page, I got Server is not available error
message and it is shown as aspnet_wp.exe stopped unexpectly error in event
log, or sometimes I get NullReferenceException from aspnet_wp. I tried run
aspnet_regiis -i and aspnet_regiis -i -enable. It does not help at all.I am
running on Win XP SP2. Thanks for your hel in advance.

Shirley