Consider the following scenario. In Internet Information Services (IIS) 7.0 that is running on a 32-bit operating system, you create a new application pool or try to modify an existing application pool. You configure the application pool to use the Microsoft .NET Framework 1.1. In this scenario, the Managed Pipeline Mode box is not available.
Note When you create an application pool in IIS 7.0, the default value for the Managed Pipeline Mode setting is Integrated. The Integrated value is not supported by Microsoft ASP.NET 1.1 in the .NET Framework 1.1.
This problem occurs because of a defect in Server Manager.
To resolve this problem when you create a new application pool, set the Managed Pipeline Mode setting to Classic before you set the .NET Framework Version setting to v1.1.
To resolve this problem when you modify an existing application pool that uses the .NET Framework 1.1, change the .NET Framework Version setting to v2.0. After you change the .NET Framework Version setting to v2.0, change the Managed Pipeline Mode setting to Classic. Then, change the .NET Framework Version setting to v1.1.
This issue does not apply to 64-bit operating systems. If you are running IIS 7.0 on a 64-bit operating system, by default, IIS Manager does not give you an option to configure the application pool to use the .NET Framework 1.1 because ASP.NET 1.1 is not supported to run under the 64-bit IIS worker process.
Note When you install the .NET Framework 1.1 on a 64-bit operating system, it creates an application pool that is named the ASP.NET 1.1 application pool. Additionally, it changes the ApplicationHost.config file to run this application pool under the .NET Framework 1.1 and classic mode with the enable 32-bit applications property (the enable32bitAppOnWin64 property) set to TRUE.
When you run an ASP.NET 1.1 application in managed mode, the application may generate random errors or may not work at all.
Steps to reproduce the problem
Start Server Manager.
Expand the server name, and then click Application Pools.
Under Actions, click Add Application Pool.
Type a name for the application pool.
In the .NET Framework Version box, click .NET Framework 1.1.
Note You must install the .NET Framework 1.1. The .NET Framework 1.1 is not included when you install Windows Server 2008.
Notice that the Managed Pipeline Mode box is not available.