@Jackson
There's no need to downgrade the kernel anymore. The workaround, which I use on my C720 and it works is:
1. Open the file /etc/default/grub as root in a text editor with: gksu gedit /etc/default/grub
2. change the line: GRUB_CMDLINE_LINUX_DEFAULT="tpm_tis.force=1" and save changes
3. sudo update-grub
@Jackson LINUX_DEFAULT= "tpm_tis. force=1" and save changes
There's no need to downgrade the kernel anymore. The workaround, which I use on my C720 and it works is:
1. Open the file /etc/default/grub as root in a text editor with: gksu gedit /etc/default/grub
2. change the line: GRUB_CMDLINE_
3. sudo update-grub