Came across this problem when trying to install validate the Report Server whilst trying to install CRM on Windows 2003/SQL Server 2005 Machine.
It turns out that this error was due to installing the .net framework before the IIS was installed.
By re-registering/reinstalling the IIS v.2.blah.blah Framework, the Reporting Server kicked into life.
Use the following syntax below to do this inside the Command Prompt.
%Windir%\Microsoft.NET\FRAMEWORK\V2.0.50727\aspnet_regiis.exe -i
Enjoy
Jonathan