Ubuntu 14.04 Лохин Лооп - need to поверьте new user after every reboot?

гm running ubuntu 14.04 on в виртуальный box within в windows 8 host machine. гve had the misfortune of stumbling upon the dreaded ubuntu 14.04 login loop after в sudo apt-get upgrade command, and have tried all suggestions (checking.Xauthority, reinstalling lightdm, installing alternative desktop programs, и т.д....) and the only approach that существуешь actually worked was to add в new user (with superuser privileges). Unfortunately, this only works одиннадцать... After I reboot the computer, the login loop ты обобщаешь and the newly created user не longer allows я to login successfully. Everytime I reboot, I need to add в new user with superuser privileges in order to login successfully.

So, I have two questions:

1. Why does adding в new user work at all (even if only одиннадцать)? What exactly is it temporarily fixing.
2. The fact that the login loop ты обобщаешь after reboot on the newly created user is в symptom of в deeper problem, imho. What exactly is the deeper problem and how хан I fix it?