I had this problem too, during installation...
[Errno 5] Input/output error
Target machine was a brand new Asus K53e laptop. Installation image was ubuntu-11.10-desktop-amd64.iso (64-bit). I burned this image to CD... Errno 5. Burned it to bootable USB stick... Errno 5 again :( I tried 4 or 5 times.
fsck said the entire root partition was fine (after 10 hours). memtest86+ said all 6GB of RAM was fine too. I tried installing directly when the live image booted up (Install Ubuntu). I also tried the Try Ubuntu button, then ran install from the live desktop. Again, Errno 5.
In the end, it turns out the iso file I downloaded was somehow out of date or wrong. Can you believe it!?
$ md5sum ubuntu-11.10-desktop-amd64.iso
The output was different from Ubuntu's official hash (62fb5d750c30a27a26d01c5f3d8df459). Then I cast my mind back. I remember, when I downloaded this image, I think I was forwarded from ubuntu.com to a mirror site, and I chose a French one at random because my nearest UK mirror was down. It must've been slightly out of date or something. In fact, I now remember seeing entries like this
SQUASHFS error: zlib inflate error, data probably corrupt
squashfs_read_data failed to read block 0x1e457bbd
in the output of
dmesg (I think) or somewhere in
/var/log when checking after the installation crash dumped me back to the live (Try Ubuntu) desktop.
Basically, make sure you check the MD5 hash of your downloaded ISO file! (I know. I know. I rarely check either!)
Anyway,I downloaded 64-bit Ubuntu 11.10 again and, this time, I was prompted with a Save As dialog, instead of being asked to choose a mirror site. When downloaded, checksum matched :) Installation ok :)