on opening the MMC containing the IIS snap-in, a dialog box appears with the following error message / you are unable to enumerate web sites because the following error occurred :
Object already exists
here was my fix/workaround...
CAUSE
The permissions to the keys located in the \Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\Machinekeys directory have been changed.
in my circumstance, i was on a new developer box, with restricted permissions. even after admin permission on the local box was granted, i still got this error.
RESOLUTION
under advanced security properties for the "\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\MachineKeys", i enabled the checkbox 'allow inheritable permissions to from parent to propagate to this object'
see :
http://support.microsoft.com/default.aspx?scid=kb;en-us;246459