Technique Microsystems Ltd.

Although it is possible to run the .NET Framework 1.1 on x64 editions of Windows, you may be surprised to find that your IIS6 applications start failing with the following errors if you also have Exchange 2007 installed:

Event Type: Error
Event Source: WSVC
Event ID: 1039
Description: process serving application pool 'DefaultAppPool' reported a failure. The process id was '2696'. The data field contains the error number.

Event Type: Error
Event Source: W3SVC
Event ID: 1002
Description: Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool.

According to this Microsoft article Exchange 2007 requires the .NET Framework 2.0 (which supports both 32-bit and 64-bit modes) to run in 64-bit mode, while the .NET 1.1 Framework runs only in 32-bit mode. Unfortunately for IIS6 to run both frameworks simultaneously, it must be running in 32-bit mode. Since only the 64-bit edition of Exchange 2007 is supported in a production environment it won't be possible to use any of your .NET 1.1 applications on your production Exchange 2007 server.