Here you specify the os users that will be able to administer the server. there are 3 that must always be present in this list. NT Authority\SELF, NT Authority\SYSTEM, and the user the service is running as (or only 2 if the LocalSystem is selected as the user it is to run as). Sometimes the permissions might get damaged such that you can not administer the server. If that happens you must reset the permissions to allow administration from within the DCOMCNFG.EXE tool provided by microsoft.