Comment 9 for bug 236307

There might be several causes for busybox. A common one is that the Windows file system has the dirty flag set, in which case you need to clear it by booting into Windows, running chkdsk /r and rebooting cleanly.

That said if you can boot with an older kernel (press ESC at boot after selecting "Ubuntu") but not with a newer one, the issue is probably different.

Andrew the message

/dev/disk/by-uuid/2E0E-0CE2 on /root failed: No such device

is a good lead. You can interrupt the boot process using the kernel argument:

break=mount

You will end up in a busybox at the point where the device has to be mounted and investigate why the root device is not available.

It would be also interesting to have confirmation from other users whether in their experience the issue is also due to the root device not being available.