What happens is that the system runs fine for several days or even a week and then suddenly the root file-system / goes read-only. Looking at the syslog it shows that there was an 'Unhandled sense code'. This is under Ubuntu 10.04 but I saw the same thing with Ubuntu 9 with different flash media.

/dev/sdg1 on / type ext4 (rw,errors=remount-ro)

Jun 26 08:50:04 host1 kernel: [926247.565090] sd 5:0:0:0: [sda] Unhandled sense code Jun 26 08:50:04 host1 kernel: [926247.565094] sd 5:0:0:0: [sda] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jun 26 08:50:04 host1 kernel: [926247.565098] sd 5:0:0:0: [sda] Sense Key : Data Protect [current] Jun 26 08:50:04 host1 kernel: [926247.565103] sd 5:0:0:0: [sda] Add. Sense: Write protected Jun 26 08:50:04 host1 kernel: [926247.565108] sd 5:0:0:0: [sda] CDB: Write(10): 2a 00 00 46 29 18 00 00 08 00 Jun 26 08:50:04 host1 kernel: [926247.565117] end_request: I/O error, dev sda, sector 4598040 Jun 26 08:50:04 host1 kernel: [926247.569788] Buffer I/O error on device sda1, logical block 574499 Jun 26 08:50:04 host1 kernel: [926247.574677] lost page write due to I/O error on sda1