I use Ubuntu 16.04 under VirtualBox. Today I updated VirtualBox to 5.0.26. After it I updated the Ubuntu using GUI, but the update has frozen during grub update. After reset, it started normally and I finished the update manually from command line.
Now, after logging in the Unity does not start. I can reach the terminal via popup menu and start the Unity manually via the terminal using "unity -v" command. Interestingly without the "-v" option the unity does not start. I tried to reinstall unity and this without success. Any idea?
I finally found the solution on this page:
this worked for me: