Did the kernel 4.7 upgrade on my playtime box and got the same problem.
Error text and won't boot.
Followed the instructions on jxself site on a fully up-to-date Trisquel 7
install previously running the 3.13 "linux-generic" default kernel.
Error text during boot after the upgrade:
/scripts/init-top/udev: line 14: can't create /sys/kernel/uevent_helper:
Permission denied
mdadm: CREATE group disk not found
mdadm: CREATE group disk not found
mdadm: CREATE group disk not found
mdadm: CREATE group disk not found
Video card is ATI HD6450
