OS malfunction

I ran sfc /scannow because of a possible corrupt file. When Windows File
Protection started I got the message "Files that are required for Windows to
run properly must be copied to the DLL cache." It then instructed, "Insert
your Windows XP Professional Service Pack 2 CD now." I don't get it, I have
Windows XP Home Edition and that's what the OS disk say's. Needless to say,
the process didn't work because when I ran sfc /scannow again I got the same
message. Can anybody shed any light on this anomoly. (I had uninstalled
Service Pack 3 so the OS disk would match what was on the C: drive). I have a
Vostro 200 desktop system. Thanks for any assist.
Dave G.