Same problem here. Windows 7 support gives several so-called fixes (including regedit tweaks, eliminating the blocked user account), but all require access to that partition. So far as I know, I have only one user, since this is my personal computer -- unless there is some sort of default "administrator" logon.
Windows support says the problem might be caused by antivirus software running while we try to logon, but this problem has never happened to me before, and I have not made anti-virus changes (maybe AVG or Avast did so automatically)
I tried to access regedit through Finder, but get a garbled text-edit with the message that regedit cannot be opened by DOS.
So I wonder (a) is there a default admin logon? (b) Can we tinker with the settings inside Windows from Finder, or (c) how else can we get into Windows?
My setup: Macbook Pro (Fall 2010), 10.6.8, boot camp, Windows 7.