How to Configure Different Versions of an ASP.NET Application Running on the Same Web Server

Here is an excerpt from the KB article: KB 816782

Find the ASP.NET Version Used for the Application
View the script map for an ASP.NET application to determine the version of ASP.NET that the application uses. To view the script map for an ASP.NET application, follow these steps:

1. Click Start, point to Programs, and then click Control Panel.
2. Double-click Administrative Tools, and then double-click Internet Information Services (IIS).
3. Expand local computer, expand Web Site, and then expand Default Web Site.
4. Locate the folder that contains the ASP.NET application.
5. Right-click the folder that contains the ASP.NET application, and then click Properties.
6. Click the Directory tab, and then click Configuration. The Application Configuration dialog box opens.
7. Click the Mappings tab, and then select an ASP.NET application extension, such as .asmx or .aspx.
   The Executable Path column of the dialog box lists the path to the ASP.NET ISAPI version that the application uses. By default, the ASP.NET ISAPI is installed in %WindowsDirectory%\Microsoft.NET\Framework\%versionNumber%. The version number in the path indicates the version number of the ASP.NET ISAPI that the application uses. The ASP.NET ISAPI version determines the version of the runtime that the application uses.

Use Aspnet_regiis.exe to Update the Script Map
To make it easier to reconfigure the script map for an ASP.NET application, each installation of the .NET Framework is associated with a version of the ASP.NET IIS Registration tool (Aspnet_regiis.exe). You can use this tool to remap an ASP.NET application to the ASP.NET ISAPI version associated with the tool.

Note Because Aspnet_regiis.exe is linked to a specific version of the .NET Framework, you must use the appropriate version of Aspnet_regiis.exe to reconfigure the script map for an ASP.NET application. Aspnet_regiis.exe only reconfigures the script map of an ASP.NET application to the ASP.NET ISAPI version associated with the tool

Configure ASP.NET 1.0 for the Application
When ASP.NET 1.1 is configured on the root Web site, follow these steps to configure ASP.NET 1.0 for an application:

1. Click Start, and then click Run. In the Open text box, type cmd, and then click OK.
2. At the command prompt, locate the following directory path:
   %WindowsDirectory%\Microsoft.NET\Framework\v1.0.3705\
3. Type the following command to configure the ASP.NET 1.0 application in IIS:

   
   aspnet_regiis -s w3svc/1/root/ApplicationName 
   

   To remove ASP.NET 1.0 from this application, repeat steps 1and 2, and then type the following command:

   
   aspnet_regiis -k w3svc/1/root/ApplicationName
   

Configure ASP.NET 1.1 for the Application
When ASP.NET 1.0 is configured on the root Web site, follow these steps to configure ASP.NET 1.1 to run an application:

1. Click Start, and then click Run. In the Open text box, type cmd, and then click OK.
2. At the command prompt, locate the following directory path:
   %WindowsDirectory%\Microsoft.NET\Framework\v1.1.4322
3. If ASP.NET 1.1 is not already registered, type the following command to register it:
   aspnet_regiis -ir
   Note The -ir option registers ASP.NET 1.1 without updating the scripts in IIS.
4. Type the following to configure the ASP.NET 1.1 application in IIS:

   
   aspnet_regiis -s w3svc/1/root/ApplicationName 
   

   To remove ASP.NET 1.1 from this application, repeat steps 1 and 2, and then type the following command:

   
   aspnet_regiis -k w3svc/1/root/ApplicationName