missing sp2 files

I have a w2k server using activie directory and has servivce pack 2 installed. Its been reported that some mornings theres a message saying some service pack 2 files missing and asking service pack 2 cd rom. It gives option to cancell or insert cdrom. It also say if cancell system my become instable. So far error message is cancelled to continue working. Should I reinstall service pack 2 and will I have to reinstall drivers or will it change any users id info thanks