This means that ASP.Net is not properly registered with IIS.
.Net framework provides an Administration utility that manages the installation and uninstallation of multiple versions of ASP.NET on a single machine. You can find the file in C:\WINNT\Microsoft.NET\Framework\v**\aspnet_regiis.exe
use the command: aspnet_regiis.exe -u ---> to uninstall current asp.net version. use the command: aspnet_regiis.exe -i ---> to install current asp.net version.
For Windows Server 2003, you must use aspnet_regiis -i -enable
This is because of the ‘Web Service Extensions’ feature in IIS 6
(if you install VS.NET or the framework without IIS installed, and then go back in and install IIS afterwards, you have to re-register so that ASP.NET ’hooks’ into IIS properly.’