This seems to be only a wrong checksum of a download, but may be not the cause for the failed install. 

Later on in UbiquitySyslog.txt there are segmentation faults recorded:

Sep  2 06:10:17 ubuntu grub-installer: info: architecture: amd64/generic
Sep  2 06:10:18 ubuntu grub-installer: info: Identified partition label for /dev/sda1: msdos
Sep  2 06:10:18 ubuntu kernel: [  652.195546] debconf-set-sel[19209] general protection ip:7f2af2a722a2 sp:7fffaf4eb170 error:0 in libperl.so.5.14.2[7f2af29ae000+173000]
Sep  2 06:10:24 ubuntu ubiquity: Segmentation fault (core dumped)
Sep  2 06:10:37 ubuntu grub-installer: info: architecture: amd64/generic
Sep  2 06:10:38 ubuntu grub-installer: info: Identified partition label for /dev/sda1: msdos
Sep  2 06:10:38 ubuntu kernel: [  671.982462] debconf-set-sel[19318] general protection ip:7f79018a15a1 sp:7fff9d0486b0 error:0 in libperl.so.5.14.2[7f79017e8000+173000]
Sep  2 06:10:38 ubuntu ubiquity: Segmentation fault (core dumped)
Sep  2 06:10:42 ubuntu grub-installer: info: architecture: amd64/generic
Sep  2 06:10:42 ubuntu grub-installer: info: Identified partition label for /dev/sda1: msdos
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-legacy
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-efi
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-efi-amd64-bin
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-efi-amd64
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-efi-ia32-bin
Sep  2 06:10:43 ubuntu grub-installer: dpkg: warning: there's no installed package matching grub-efi-ia32
Sep  2 06:10:44 ubuntu grub-installer: info: Installing grub on '/dev/sda'
Sep  2 06:10:44 ubuntu kernel: [  677.716906] lsb_release[19543] general protection ip:7f269d40528f sp:7fffef448d30 error:0 in ld-2.15.so[7f269d3f9000+22000]
Sep  2 06:10:44 ubuntu grub-installer: info: grub-install supports --no-floppy
Sep  2 06:10:44 ubuntu grub-installer: info: Running chroot /target grub-install  --no-floppy --force "/dev/sda"
Sep  2 06:10:44 ubuntu kernel: [  677.852178] lsb_release[19587] general protection ip:7fa111a6128f sp:7fffe1c8c330 error:0 in ld-2.15.so[7fa111a55000+22000]
Sep  2 06:10:47 ubuntu grub-installer: Installation finished. No error reported.
Sep  2 06:10:47 ubuntu grub-installer: info: grub-install ran successfully
Sep  2 06:10:49 ubuntu ubiquity: Setting partition 1 of /dev/sda to active... done.
Sep  2 06:10:50 ubuntu kernel: [  684.152877] lsb_release[19996] general protection ip:7fb88421c28f sp:7fffb4e1c410 error:0 in ld-2.15.so[7fb884210000+22000]
Sep  2 06:10:54 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda2
Sep  2 06:10:54 ubuntu 50mounted-tests: debug: /dev/sda2 type not recognised; skipping
Sep  2 06:10:54 ubuntu os-prober: debug: os detected by /usr/lib/os-probes/50mounted-tests
Sep  2 06:10:54 ubuntu os-prober: debug: /dev/sda5: is active swap
Sep  2 06:10:54 ubuntu plugininstall.py: log-output -t ubiquity umount -f /target/proc
Sep  2 06:10:54 ubuntu plugininstall.py: log-output -t ubiquity umount -f /target/sys
Sep  2 06:10:54 ubuntu plugininstall.py: log-output -t ubiquity umount -f /target/dev
Sep  2 06:10:56 ubuntu kernel: [  690.274407] plugininstall.p[9015]: segfault at 3c307ab0 ip 00007fa3130515b9 sp 00007fffd234cfd0 error 4 in libapt-pkg.so.4.12.0[7fa312ffd000+120000]
Sep  2 06:12:10 ubuntu ubiquity: 
Sep  2 06:12:10 ubuntu ubiquity: ** (apport-gtk:20373): WARNING **: The connection is closed