From UbiquitySyslog.txt which has been added to this bug report:
May 6 21:23:37 ubuntu kernel: [ 392.877357] SQUASHFS error: zlib decompression failed, data probably corrupt
May 6 21:23:37 ubuntu kernel: [ 392.877362] SQUASHFS error: Failed to read block 0x4b2d83c: -5
It's possible you had a bad write to your installation media or for some other reason its contents could not be read correctly. If you've tried again and are still having problems you should try re-writing the image to your media (and maybe re-download the image as well).
From UbiquitySyslog.txt which has been added to this bug report:
May 6 21:23:37 ubuntu kernel: [ 392.877357] SQUASHFS error: zlib decompression failed, data probably corrupt
May 6 21:23:37 ubuntu kernel: [ 392.877362] SQUASHFS error: Failed to read block 0x4b2d83c: -5
It's possible you had a bad write to your installation media or for some other reason its contents could not be read correctly. If you've tried again and are still having problems you should try re-writing the image to your media (and maybe re-download the image as well).