system.cannotunloadappdomain

My system is Windows 2000 SP4 and .NET 1.1
After i upgraded to .NET 2.0, error occured.

Error from Event Viewer:

Event Type: Error
Event Source: ASP.NET 2.0.50727.0
Event Category: None
Event ID: 1000
Date: 7/17/2008
Time: 5:48:07 PM
User: N/A
Computer: AACMSAPP1
Description:
aspnet_wp.exe (PID: 1424) stopped unexpectedly.

Event Type: Error
Event Source: .NET Runtime 2.0 Error Reporting
Event Category: None
Event ID: 5000
Date: 7/17/2008
Time: 5:48:00 PM
User: N/A
Computer: AACMSAPP1
Description:
EventType clr20r3, P1 aspnet_wp.exe, P2 2.0.50727.213, P3 450b6662, P4
mscorlib, P5 2.0.0.0, P6 4333ab80, P7 482, P8 27, P9
system.cannotunloadappdomain, P10 NIL.

I found that the Description means:
P1 - Proc Name - aspnet_wp.exe
P2 - Version - 2.0.50727
P3 - Timestamp - 450b6662
P4 - Asembly Name - mscorlib
P5 - Assembly Version - 2.0.0.0
P6 - Assembly Timestamp - 4333ab80
P7 - Unknown - 482
P8 - Unknown - 27
P9 - Namespace? - system.cannotunloadappdomain
P10- Unknown - NIL

I have tested for many servers, only the production server has this
issue.
I have already reinstall IIS 5, .NET 2.0 and run the
aspnet_regiis.exe,
and iisreset. The problem still here...

I have found information about appdomain,
i think the problem is closely related to the configuration of the
application domain,
but i don't know to to unload or creating a new appdomain for my
application.
Is it necessary to write a new page to unload and create the
appdomain?

Any suggestions for this issue? Thanks.