The Windows 2000 –> Windows XP upgrade had a small problem. When you tried to remote access the registry, the now Windows XP would tell you “Permission Denied”.
Microsoft documented the fix in KB892192.
By default, Windows 2000 does not have a built-in user account named Local Service. Instead, the Remote Registry Service is logged on as Local System. In Windows XP, the Remote Registry Service is logged on as Local Service.
One way to fix it, is to use the REGPERM utility, with a command line like this:
c:\winnt\system32\regperm.exe /k "hkey_local_machine\SYSTEM CurrentControlSet\Control\SecurePipeServers\winreg"" /E /a:"Local Service":R /I