From today morning we start recieving very weired probelm, i hope any techie guy will help me to resolve this. Last day we push Windows Vista SP2 to all client machines through WSUS, but Service pack gets failed to upgrade on all client machines. After that today morning we realized that most of the client machines stopped communicate with Active Directory (ADDS, DNS and DHCP Service), then we identified that DHCP client Service stopped and could not start. Error: "Windows could not start the DHCP Client service on Local Computer. Error 5:Access is denied" After some forums and threads we got workaround for issue but that need to be perform on each and every machines and we have approx 500 users including remote sites. for workaround i followed this post and run this below command on one of effected machine "NETLOCALGROUP administrators "NT Authority\Local Service" /add" and DHCP client service start working, another wiered is i tried to upgrade SP2 on another effected machine and again it gets failed but the magic is DHCP client service started even after SP2 failed So i dont understand what to do to resolve for 500 users, whether to go with SP2 upgrade even after knowing that it will get failed or run that command.

Are you using a Norton security product?

no we are using McAfee product, but the problem is resolved now.