Comment 3 for bug 739969

Sorry about that, there is some useful information in UbiquitySyslog.gz:

Mar 22 05:18:04 ubuntu kernel: [ 5326.940623] ata1.00: status: { DRDY ERR }
Mar 22 05:18:04 ubuntu kernel: [ 5326.940625] ata1.00: error: { UNC }
Mar 22 05:18:04 ubuntu kernel: [ 5326.941428] ata1.00: SB600 AHCI: limiting to 255 sectors per cmd
Mar 22 05:18:04 ubuntu kernel: [ 5326.942466] ata1.00: SB600 AHCI: limiting to 255 sectors per cmd
Mar 22 05:18:04 ubuntu kernel: [ 5326.942469] ata1.00: configured for UDMA/133
Mar 22 05:18:04 ubuntu kernel: [ 5326.942483] sd 0:0:0:0: [sda] Unhandled sense code
Mar 22 05:18:04 ubuntu kernel: [ 5326.942486] sd 0:0:0:0: [sda] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
Mar 22 05:18:04 ubuntu kernel: [ 5326.942490] sd 0:0:0:0: [sda] Sense Key : Medium Error [current] [descriptor]
Mar 22 05:18:04 ubuntu kernel: [ 5326.942496] Descriptor sense data with sense descriptors (in hex):
Mar 22 05:18:04 ubuntu kernel: [ 5326.942498] 72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
Mar 22 05:18:04 ubuntu kernel: [ 5326.942507] 00 69 0a ba
Mar 22 05:18:04 ubuntu kernel: [ 5326.942511] sd 0:0:0:0: [sda] Add. Sense: Unrecovered read error - auto reallocate failed
Mar 22 05:18:04 ubuntu kernel: [ 5326.942517] sd 0:0:0:0: [sda] CDB: Read(10): 28 00 00 69 0a b3 00 00 08 00
Mar 22 05:18:04 ubuntu kernel: [ 5326.942526] end_request: I/O error, dev sda, sector 6884026
Mar 22 05:18:04 ubuntu kernel: [ 5326.942543] ata1: EH complete
Mar 22 05:18:04 ubuntu kernel: [ 5326.942569] EXT4-fs error (device sda4): ext4_find_entry: reading directory #134944 offset 0
Mar 22 05:18:04 ubuntu kernel: [ 5326.942575] Aborting journal on device sda4-8.
Mar 22 05:18:04 ubuntu kernel: [ 5326.943875] EXT4-fs (sda4): Remounting filesystem read-only
Mar 22 05:18:07 ubuntu ubiquity: dpkg: error al procesar ubiquity (--purge):
Mar 22 05:18:07 ubuntu ubiquity: imposible eliminar de forma segura «/target/lib/partman/active_partition/ 65toggle_bootable/choices.dpkg-tmp»: Sistema de solo lectura
Mar 22 05:18:07 ubuntu ubiquity: dpkg: error fatal irrecuperable, abortando:
Mar 22 05:18:07 ubuntu ubiquity: no se puede efectuar `flush' con el estado actualizado de `cryptsetup': Sistema de solo lectura
Mar 22 05:18:07 ubuntu kernel: [ 5330.061807] install.py[22699]: segfault at 0 ip 0090ad40 sp bfa40a8c error 4 in libc-2.11.1.so[82a000+153000]

It looks like there were some errors in the communication with your hardware.