Вот нарыл некоторые причины и их солюшны:

These errors can be due to a variety of reasons:

* bad media (solution: try burning the iso image to a new disc)
* a bad dvd drive (solution: if possible, try using a different cd/dvd drive)
* bad memory modules (solution: use memtest86+ to check your memory)
* a corrupted iso image (solution: run an md5 checksum, and if they don't match, download the iso image again)
* an optical drive connected via SATA instead of PATA and running in Enhanced mode (solution: change the IDE configuration to "compatible" in the BIOS)

This is all described in more detail here:
https://help.ubuntu.com/community/SquashfsErrors