Grab a freebie called REVO UNINSTALLER, use it's most aggressive setting to
remove your old version of ADR and any signs of the new one. Also get and
use a Windows Registry Cleaner (if you have other Autodesk products, be
prepared to reinstall them).
Restart Windows, try a new install.
"0x643: Internal Error" is a Windows system problem related to the Registry
from what I understand.
--
Dean Saadallah
http://LTisACAD.blogspot.com--