USB drive errors

Hey everyone, I've been having some problems with a USB keychain drive.

By default my HDD install of Knoppix did not allow me to auto-detect or mount USB devices (particularly from Konqueror), so I created the directory /mnt/usb and added this line to /etc/fstab

/dev/sda1 /mnt/usb auto defaults,user,noexec,auto 0 0

At first when I only tried reading from the drive everything seemed to work fine, I could mount, unmount and access the drive from the devices tab in Konqueror. However, when I try to copy something to the drive, the copy may only be partially successful (my first copy was 2 files, one good and one corrupted). After this point I can no longer unmount the drive. umount -f gives the following error:

root@monster:/home/matt# umount -f /mnt/usb
umount2: Device or resource busy
umount: /dev/sda1: not mounted
umount: /mnt/usb: Illegal seek

To access the USB drive again I have to reboot the machine.

I'd appreciate any suggestions on how to fix the problem, and also any advice on how to force an unmount if this problem comes up again (or for testing out solutions, so I don't have to reboot for each one).

One other thing: I just realized that /mnt/usb is owned by my normal user account and not root, could this be a problem?


Complete /etc/fstab:

# /etc/fstab: filesystem table.
#
# filesystem mountpoint type options dump pass
/dev/hda3 / ext3 defaults,errors=remount-ro 0 1
/dev/hda2 none swap sw 0 0
proc /proc proc defaults 0 0
/dev/fd0 /floppy vfat defaults,user,noauto,showexec,umask=022 0 0
/dev/cdrom /cdrom iso9660 defaults,ro,user,noexec,noauto 0 0
/dev/dvd /dvd iso9660 defaults,ro,user,noexec,noauto 0 0
/dev/cdaudio /cdaudio iso9660 defaults,ro,user,noexec,noauto 0 0
# Added by KNOPPIX
/dev/hda1 /mnt/hda1 ext2 noauto,users,exec 0 0

# TEST - USB drive
/dev/sda1 /mnt/usb auto defaults,user,noexec,auto 0 0