Server failed to load application

This week we rolled out Windows XP migration to all our PCs. I had to reinstall all the tools that I have been using since it is not part of the SOE. Everything was fine , eventhough reinstalling Visual Studio .Net took almost half a day , until I tried to run one of my ASP.Net project.

It just doesn't want to run. After turning off the "show friendly error" in IE, it displayed the error message "Class is not registered".

Next, I checked the IIS extension mapping, there is no ASPX registered there. So, I reinstalled ASP.Net by running the command "aspnet_regiis -i". Still doesn't want to run.

After googling for a while, I found this link. It told me to recreate IIS Package, so did I. Indeed, it start to work again.