post scriptum. after saving files, i gave it one more try, it managed to revert back to 10041 and works ok again both as native vhd boot and inside vm. switched to slow ring waiting for next fast ring build.
Update: OK, I tried 1 last time and after too many hrs. it got all the way to 80% (that's an improvement over the 79% before So I found a version 10056, created a new VM on VMWare Workstation and did a fresh install. It's only been a day or so, but seems to be working fine. It was a bit of a bothersome nuisance to have to reload the few applications I had running under 10041 Maybe next time will be a smoother upgrade.... Cheers....