I have seen the other posts regarding this error message but all seem to relate to domains and remote access. I now have a desktop computer that I can no longer log onto with any of the previously valid user names, including administrator and guest, including in safe mode. I have run Windows repair and replaced the Security file with the version in the Repair directory. Using Repair Console I have run secedit to reset to default security settings, all to no avail. Can anybody offer any suggestions as to what might have happened and how to correct it?