Upgrade failed with the same error code. I uploaded fresh setupact.log to the same Dropbox folder (subfolder "3rd try (...)"). It looks like the same error. "Lenovo" vs "Lenovo.000" conflict.
During upgrades, while you're guiding me, I always choose 1) not to download updates etc. and 2) preserve my apps and settings. (Although I tried various combinations before I created this thread).
Could it be a possible solution if I created a new user named "Lenovo.000"? And maybe copy my userprofile content there (or maybe leave it unchanged after creation)? Or something in this direction?