A very common but weird error when trying to open asp.net applications using visual studio.net is "Visual Studio has detected that the specified Web Server is not running ASP.NET version 1.1. You will be unable to run ASP.NET Web applications or services."
 
This will paralyze you particularly if you have been working on some applications for sometime and one fine morning when you open vs.net, you get this message.
 
The resolution is simple, just re-register the aspnet user account.  To do that, type the following from your command prompt:-
 
c:\Windows\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis.exe -i

This will install the aspnet user account and register the asp.net with the IIS.