Comment 7 for bug 268356

SD-card with 2 partitions:
$ ls -l /media
total 7
lrwxrwxrwx 1 root root 6 2008-03-12 12:46 cdrom -> cdrom0
drwxr-xr-x 2 root root 4096 2008-05-07 15:31 cdrom0
drwx------ 4 excogitation root 1536 1970-01-01 01:00 disk
drwxr-xr-x 17 root root 1024 2008-06-21 11:58 disk-1

I played around with it a bit more and I think the error (now?) only occurs on SD-cards with multiple partitions.
$ gnome-mount -b -v -u -d /dev/sdb1
gnome-mount 0.8
** (gnome-mount:24678): DEBUG: Unmounting /org/freedesktop/Hal/devices/volume_uuid_481F_CDCE
** (gnome-mount:24678): DEBUG: Setting up 750ms timer for Flushing Cache dialog
** (gnome-mount:24678): DEBUG: in unmount_done : user_data = 0x0
** Message: Unmount failed for /org/freedesktop/Hal/devices/volume_uuid_481F_CDCE: org.freedesktop.Hal.Device.Volume.UnknownFailure : Cannot remove directory

 -> error

$ gnome-mount -b -v -u -d /dev/sdb2
gnome-mount 0.8
** (gnome-mount:24691): DEBUG: Unmounting /org/freedesktop/Hal/devices/volume_uuid_1f44940d_4650_40d0_ae8e_afd45da8814d
** (gnome-mount:24691): DEBUG: Setting up 750ms timer for Flushing Cache dialog
** (gnome-mount:24691): DEBUG: in unmount_done : user_data = 0x0
** Message: Unmount failed for /org/freedesktop/Hal/devices/volume_uuid_1f44940d_4650_40d0_ae8e_afd45da8814d: org.freedesktop.Hal.Device.Volume.UnknownFailure : Cannot remove directory

 -> error

Standard SD-card:$ ls -l /media (named 0151024EUR5)
total 20
drwx------ 5 excogitation root 16384 1970-01-01 01:00 0151024EUR5
lrwxrwxrwx 1 root root 6 2008-03-12 12:46 cdrom -> cdrom0
drwxr-xr-x 2 root root 4096 2008-05-07 15:31 cdrom0

$ gnome-mount -b -v -u -d /dev/sdb
gnome-mount 0.8
** (gnome-mount:22768): DEBUG: Unmounting /org/freedesktop/Hal/devices/volume_uuid_CC76_8152
** (gnome-mount:22768): DEBUG: Setting up 750ms timer for Flushing Cache dialog
** (gnome-mount:22768): DEBUG: in unmount_done : user_data = 0x0
Unmounted /dev/sdb

-> no errors (works as it should)

$ gnome-mount -b -v -u -d /dev/sdb
gnome-mount 0.8
** (gnome-mount:22780): DEBUG: Unmounting /org/freedesktop/Hal/devices/volume_uuid_CC76_8152
** (gnome-mount:22780): DEBUG: Setting up 750ms timer for Flushing Cache dialog
** (gnome-mount:22780): DEBUG: in unmount_done : user_data = 0x0
** Message: Unmount failed for /org/freedesktop/Hal/devices/volume_uuid_CC76_8152: org.freedesktop.Hal.Device.Volume.NotMounted : According to HAL, the volume is not mounted

-> different errror (also occurs when you doubleclick on the unmount icon in nautilus)