I had virtual pc with a virtual windows xp running with the default user name of "user" & no password.
It was working without issue.
I tried to change the user name to "Jerry" thru the user accounts menu within the running virtual xp machine.
Then I couldn't log on with either "User" or "Jerry". I would get bad user name or password.
I uninstalled both the the virtual windows XP and the virtual pc KB958559-x86 and then tried to reinstall.
When I try to install KB958559 I get "Installer encountered and error:0x8007052e" "Login failure: Unknown user name or bad password". It doesn't even ask for one.
I have tried a system restore to a point before the original installation of virtual PC and still the same error. I googled this but found nothing that seemed to address this issue.