Just downloaded and installed the official version. The same problems encountered with RC3 occured. See
https://www.avrfreaks.net/index.p...
After taking some 20 minutes with the HDD led fullly on (meanwhile JAVA updated, is this part of the install??) and unable to cancel the install (cancel button greyed out) I killed the install from the task manager.
Reinstalling again brought up the same error 1706 screen but this time the installation completed after installing a signed driver.