unable to run command aspnet_regiis in Visual Studio 2010 Beta command prompt

Question

Hi
Iam getting an error when trying to install asp .net through the visual studio command prompt :
"An error has occurred: 0x8007b799
You must have administrative rights on this machine in order to run this tool."
Iam getting this error even though I have logged in as an administrator user. Iam not what are the administrative rights required for installing asp .net 
My OS is  Windows 7 professional.
Can any one help on this please ?