Trying to restore USB key fails topic

Last weekend I got my first ever car stereo that has an USB port. Hooray I thought and ran off to copy some music to a memory stick.
It worked beautifully and I drove around listening to some great tracks.
Yesterday I copied five more tracks to the stick, clicked the eject button and pulled it out. Now the stereo cannot detect any music at all.
I tried deleting the partition with gparted but that failed. See here:
https://picasaweb.google.com/1021301...eat=directlink


I ran

Code:

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sudo fsck.vfat -r /dev/sdb1

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which found some bad files and made them (IIRC) zero length.
I ran

Code:

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sudo dosfsck -w -r -l -a -v -t /dev/sdb1

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which found and relocated some clusters.

Still not working correctly even though I could play some tracks on my laptop.
I ran testdisk which found the partition OK but did not make any difference. If I try copying to the drive it goes read-only.

So now I try fdisk

Code:

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#fdisk -l
Disk /dev/sdb: 8019 MB, 8019509248 bytes
134 heads, 28 sectors/track, 4174 cylinders, total 15663104 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

  Device Boot      Start        End      Blocks  Id  System
/dev/sdb1            2048    15663103    7830528  83  Linux

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Code:

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# fdisk /dev/sdb

Command (m for help): d
Selected partition 1

Command (m for help): d
No partition is defined yet!

Command (m for help): n
Partition type:
  p  primary (0 primary, 0 extended, 4 free)
  e  extended
Select (default p):
Using default response p
Partition number (1-4, default 1):
Using default value 1
First sector (2048-15663103, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-15663103, default 15663103):
Using default value 15663103

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

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I rebooted and tried again but got the same result, something is keeping the device busy and all the mp3s are still intact on the drive :(
Any ideas why?