Try Upgrading kernel... It seems there may well be some kernel/usbserial bugs in the ubuntu 2.6.15 kernel that is screwing up ttyUSB connections. See the following Ubuntu bug: https://launchpad.net/distros/ubuntu/+source/linux-source-2.6.15/+bug/39518 -- Pb syncing treo 650 on dapper drake https://launchpad.net/bugs/38574