Win 2k SP4 setup error

I wonder if you have encountered this problem. I am having trouble installing service pack 4 on some win2k sp3 workstations. The error is the following: Service Pack 4 Setup could not backup registry key HKLM\SOFTWARE\CLASSES\INTERNET.HHCTRL\CLSID to file C:\WINNT\$NTSERVICEPACKUNINSTALL$\REG00160. 5: Access is denied.
The main reason I am having to install SP4 is that some Win2k workstations are having “The memory could not be read” errors. According to Microsoft Knowledge Base Article – 262490, the latest service pack has to be installed. I would appreciate your help on the matter.