Sorry for reviving this old post... but I have come across the same problem...
Some of the solutions I have tried are the following:
# Remove Account Unknown (S-*) from permissions and taking ownership using my own administrator account, but firstly unchecking the inherit option, copying permissions and then removing unknown account and adding my own account and inheriting permissions for my account (laptop encountered error Missing !something! I do not recall it now but I think it had something to do with Hal.dll, weeks back... )
# So I do a Full recovery, unknown account is still there and registry has entries of the unknown account name (S-*), so I boot the system, format C: and then delete recovery partition and all other partitions, create a new partition and install windows XP all over again, unknown account still exists but the last two digits of the users' name change, it was 18, then it became 19, then after each recovery an increment is made, 20, 21, etc
# a little digging around into managing services, Dhcp client log warning found! In device manager, network drivers with IP PACKET, WAN MINIPORT and things I have never seen before are found, looking into their properties (Location: Unknown)!
# Writing ipconfig/all in command line displays connections that are unavailable in my network connections
# There is a hidden file in C drive named system.sav, should I be worried about this file? It has a log file of my installed application list, an "MBR" and other log files and some files with other extensions.
Is this normal... there is an administrator account showing up in safe mode even though my account is set to administrator... sometimes after my many many recoveries, when I show hidden files (my desktop theme gets corrupted) and services become blank!
Now when I boot my Notebook, something about large system support comes up when I use Fdisk...
Is this normal? I cannot believe it is... correct me if I am wrong... sorry for the long read...