1) UNINSTALL DirectUpdate (control panel: add/remove programs)
2) Download the PREVIOUS VERSION (4.6.1) and choose "CUSTOM INSTALL" to install it into a DIFFERENT FOLDER than your last install.
This seems to be the critical step... I chose C:\program files\DU4\ as my installation path (the installer created the new folder for me)
3) IT WORKS AGAIN
All the previous settings were still there in the registry! (DNS accounts, registration code, etc...)
Just remember, it seems to be VITAL that you put it in a new folder, and NOT in the "default installation path" (C:\program files\DirectUpdate 4 .. or whatever it would normally try to install to!)
BTW, here is the link to download version 4.6.1:
http://www.directupdate.net/download/DUSetup461.zip