Iis – System.Web.Extensions Not Found Even After Installing ASP.Net AJAX

I've run into this exact issue several times, and every time, the solution was to:

1. go to the Control Panel
2. go to the "Windows Components" area
3. remove IIS, let it uninstall
4. reboot
5. re-add IIS (make sure to include the ASP.NET stuff when you check off the boxes).
6. Run: C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis.exe -I

I spent hours debugging this at a client site once, and that was the trick. Since then, every time this has happened, this was the fix.

I'm not sure what the root cause is, but we tore the IIS configuration apart once trying to figure it out, and even had Microsoft RDC'ing into the server in question for 2 or 3 hours, and they couldn't help either.

So I write it off as an undocumented bug in ASP.NET/IIS.

Ugg my bad - this appears to be a dupe of https://serverfault.com/questions/63675/server-unavailable-and-removed-permissions-on-net-sites-after-windows-update. I checked the permissions on the directory that the service itself was contained within and all was well.

I also noticed that in the other question FileMon was used to see more detailed information on what / who was failing to access what.