USB-serial converter recognised but not mounted

[Colin Law]

I have a USB to serial converter. When I plug this in on a Ubuntu 9.04
machine it works fine. With lsusb I see

Bus 003 Device 007: ID 0403:6001 Future Technology Devices
International, Ltd FT232 USB-Serial (UART) IC

and in dmesg I see

[ 8139.812054] usb 3-2: new full speed USB device using uhci_hcd and address 7
[ 8140.020285] usb 3-2: configuration #1 chosen from 1 choice
[ 8140.022817] ftdi_sio 3-2:1.0: FTDI USB Serial Device converter detected
[ 8140.022863] usb 3-2: Detected FT232BM
[ 8140.022958] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB0

However on a Xubuntu 9.04 machine lsusb shows

Bus 001 Device 004: ID 0403:6001 Future Technology Devices
International, Ltd FT232 USB-Serial (UART) IC

which seems ok, but dmesg only shows

[ 1287.847468] usb 1-1: new full speed USB device using ohci_hcd and address 4
[ 1288.126514] usb 1-1: configuration #1 chosen from 1 choice

and the ttyUSB0 is not available.

I suspect that the fact that it is Xubuntu is not relevant.

Any suggestions on where to go from here would be much appreciated.

Colin