Note The Iis7.log file is located in the folder where Microsoft Windows is installed.
This issue occurs because a duplicate Internet Server API (ISAPI) filter is detected when you try to install the ASP.NET feature.
To resolve this issue, follow these steps:
To start IIS Manager, click Start, type Inetmgr in the Start Search box, and then click Inetmgr in the Programs list.
Expand the local computer node, double-click ISAPI Filters, and then remove all the ASP.NET filters that are listed.
Reinstall the ASP.NET feature of IIS 7.0 by using the Turn Windows Features On or Off wizard.
Steps to reproduce the behavior
On a computer that is running Microsoft Windows XP, install the Microsoft .NET Framework 2.0 and the Microsoft .NET Framework 1.1.
This step installs Microsoft ASP.NET 2.0 and Microsoft ASP.NET 1.1.
Install the security update that is described in the following Microsoft Knowledge Base article:
922770 MS06-056: Vulnerability in ASP.NET 2.0 could allow for information disclosure
When this security update is installed, the ISAPI filter that is named ASP.NET_2.0.50727.42 is renamed ASP.NET_2.0.50727.210.
Upgrade the computer to Windows Vista.
When you upgrade the computer to Windows Vista, the IIS metabase is migrated to Windows Vista. This step also installs the renamed ISAPI filter that is mentioned in step 2. When the .NET Framework 1.1 is installed, the installation program registers a duplicate ISAPI filter.
In IIS 7.0, try to install the ASP.NET feature.
When you try to install the ASP.NET feature, the ASP.NET installation file (Aspnetca.exe) detects the duplicate ISAPI filter that is mentioned in step 3. Therefore, the installation fails.