pendrive mounting problems

[Ultrakorne]

i have problems with some pendrives, my digital camera is mounted 
automatically at plug, but my friend's pen driver have problems...
no autodetection, and i am not able to mount it because /dev/sdax dont 
exist (i think should be here)

usb_storage            69824  0
scsi_mod              129600  2 ide_scsi,usb_storage
usbcore               121656  5 usb_storage,uhci_hcd,ehci_hcd,

what's wrong in my ubuntu?