'usbdevfs' is a special type, not meant to be used. When it is specified, it does not actually mount the device you told it, but a special device, which shows some of the internal info about usb. So that's not what you want to use.
You should paste in the output of your /var/log/syslog /var/log/messages, including the parts related to USB, when you unplug and replug the device.
Random guess, probably wrong, but maybe it's getting detected as another device name? So try mounting /dev/sdc1 or /dev/sdd1, etc