Trouble running any Aspx on XP-Proff.

Sorry for this .NET beginners little post .. but ..

- just installed Visual Studio .NET on WinXP Pro environment
- DirectX (managed code) + windows .NET samples run just fine
- IIS is running ( only default website on XP pro )
- I see that .aspx extension is linked to a .NET .dll

- Creating a web-application does all things like making
virtual directory on the server .. and placing files in my
default website of IIS

BUT ...

when I try to access .aspx file in Browser I get the error :
( not a beautifull .NET error message but an old one
like the system does not work at all )
....

Server Application Error

The server has encountered an error while loading an application during the processing of your request. Please refer to the event log for more detail information. Please contact the server administrator for assistance.
....

Can someone plz help me out a bit ?