64-bit system runs 32-bit program

Applications and dynamic-link libraries are best compiled under the x86 platform,

If you are a Web application, you will also need to modify the IIS configuration

64-bit systems also need to install 32-bit framework framework packages

Configuring IIS to enable 64-bit IIS to run 32-bit Web applications

1. Open the command line to navigate to the%systemdrive%/inetpub/adminscripts directory.

2. Type and execute the following command:

cscript.exe adsutil.vbs set W3svc/apppools/enable32bitapponwin64 "true"

3. If you need to revert to a running 64-bit application:
cscript.exe adsutil.vbs set W3svc/apppools/enable32bitapponwin64 "false"

The 4.Web extension allows Asp.net2.0.*32bit to run. The W3wp32.exe process is running.

http://technet.microsoft.com/zh-cn/library/cc737351