By default, in Windows 2003, ASP.Net 2.0 is not installed or enabled. You can verify this from the IIS Manager and showing the Web Service Extensions. ASP.NET v2.0.50727 is the name that should be there. If it already is, you can simply Allow it. To install it, from a command line, run the following:
64 Bit Server:
C:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727>aspnet_regiis.exe -i -enable
32 Bit Server:
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis.exe -i -enable
When you hit enter, you should see the following: Start installing ASP.NET (2.0.50727). ......................... Finished installing ASP.NET (2.0.50727).
If you refresh the Web Service Extensions, you shoud see ASP.NET v2.0.50727 enabled/allowed.