Access is denied: Unable to access rsop.msc

I upgraded my domain from Windows 2000 to Windows 2003. We currently have three DC under Win 2003.
The first one is the Primary Domain Controller and the rest are ADC.
And right now, I am facing problem on opening rsop.msc.
I keep getting “Access is denied.” Error. What should I do?

The RSoP snap-in was unable to generate the computer or user’s data due to insufficient permissions.
Details:
Access is denied.
