Re-Register ASP.Net with IIS

Windows 2000/XP
To fix this on Windows 2000 or Windows XP, run this command from the

Start>Run box or a command prompt

(assuming the system directory is C:\Documents and Settings\Administrator>):

.Net1.1: C:\Windows\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis -i
.Net2.0: C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis -i

Below Show you example with step by step to Re-Register ASP.Net with IIS in Window XP

Windows 2003
On Windows 2003, ASP.NET must be both installed and enabled. To install ASP.NET:
On the taskbar, click the Start button, point to Control Panel, and then click Add or Remove Programs.

In the Add or Remove Programs dialog box, click Add/Remove Windows Components.
In the Components box in the Windows Components Wizard, click the Web Application Server check box, and then click Next.

When the Windows Components Wizard has finished configuring Windows Server 2003, click Finish.

Run this command from the Start>Run box or a command prompt
(assuming the system directory is C:\Windows):
.Net1.1: C:\Windows\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis -i
.Net2.0: C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis -i