I apparently have the same issue.
USB connection has been a bit problematic at times: It wouldn't connect but turning the OT off & on again fixed it.
One or two times, it made the OT freeze, and one time it damaged the loaded project.
I thought it was some kind of power stability or a problem with the USB ports of my computer but it doesn't seem to be the case..
Today: nothing.
I turned the OT off & on, restarted the computer several times, retry with nothing else plugged in the USB ports, changed the USB cable, tried with the original CF card and with my old Macbook... Nothing...
I tried white magic, black magic, I played it the whole Twilight serie.. still nothing...
I begged, I prayed, I cried, I cursed (a LOT)... But she doesn't want to...
I got the No USB connection blues...
Any news on your side Giuseppe ??
Mine is 4 months old.. Should I return it to the shop ? (The OT is now my main machine: this mean almost no music while I wait for it to be repaired or to have it swap for another one..

)