In regards to the registry, the 64bit portion of the registry will be contained within the folder
Wow6432Node (i.e. HKLM\Software\Wow6432Node, HKCU\Software\Wow6432Node, etc.).
You've reached the extent of my knowledge, and if you're unable to find any fix via forums or google, I would suggest one of two options: either system restore back to a point where this was working, or do a repair install.
A repair install is where you use the Windows installation media to repair your system files. To do this, run Windows Setup from within Windows, select the option to "upgrade" and
select the option to retain all of your files and settings. What this does is replace all system files within the %WinDir%. If you have Windows 8.1, you'll need to use the Windows 8.1 installation media (not Windows 8). Once completed, you'll probably need
to re-activate Windows via PC Settings (the activation doesn't count against you)
EDIT:
Due to the nature of your issue, I'm leaning to the side of there's something else going on within your system, as the only cause, literally the only cause, of receiving an endpoint mapper error (with regards to printers) is the Windows Firewall service is not running and set to automatic. Because of this fact, I personally would do a repair install. If you have Windows 8.1, make sure you turn on every sync option for your system withinPC Settings - OneDrive - Sync Settings, as this will ensure all redundant customizations to your system are automatically copied and applied upon the OOBE that launches after the repair install is completed.