Message "Not enough disk space" although there is enough disk space on external hard disk

Hello,

since three or four days I encounter the problem described in the summary.

1.
Description: Ubuntu 12.04.1 LTS

2.
deja-dup 22.0-0ubuntu2
duplicity 0.6.18-0ubuntu3

Similar problem description from other person on forum post with no answer, yet:
http://forum.ubuntuusers.de/topic/d-j-dup-zu-wenig-platz-bei-ubuntu-one/#post-4325492

I'm using an external hard disk via USB with still 1,3 TB of free disk space. The capacity is 2 TB altogether.

For several months daily backup was working fine. But now the backup starts but is not completed. Instead the message "Not enough disk space" appears.

The external drive is formatted: msdos

3.
Checking the file
/tmp/deja-dup.gsettings

It contains:

org.gnome.DejaDup backend 'file'
# I tried to solve the problem by stepwise reducing minimum keeping time, it did not work
org.gnome.DejaDup delete-after 28
org.gnome.DejaDup exclude-list ['/home/userhome/.local/share/Trash']
org.gnome.DejaDup include-list ['/home/userhome']
org.gnome.DejaDup last-backup '2012-11-09T11:31:42.736356Z'
org.gnome.DejaDup last-restore ''
org.gnome.DejaDup last-run '2012-11-09T11:31:42.736356Z'
org.gnome.DejaDup periodic true
org.gnome.DejaDup periodic-period 1
org.gnome.DejaDup prompt-check '2012-07-23T07:33:12.727257Z'
org.gnome.DejaDup root-prompt true
org.gnome.DejaDup welcomed true
# the next two lines indicate a wrong storage type
org.gnome.DejaDup.File icon '. GThemedIcon media-flash-sd media-flash media'
org.gnome.DejaDup.File name '8,2 GB-Laufwerk (Secure Digital/Secure Digital): 8,2 GB-Dateisystem'
org.gnome.DejaDup.File path 'file:///media/VERBATIM/UBUNTU'
org.gnome.DejaDup.File relpath b''
# in fact it is a USB-Harddisk with 2 TB
org.gnome.DejaDup.File short-name '8,2 GB-Dateisystem'
org.gnome.DejaDup.File type 'normal'
org.gnome.DejaDup.File uuid 'AF7D-EAE9'
org.gnome.DejaDup.Rackspace container 'computername'
org.gnome.DejaDup.Rackspace username ''
org.gnome.DejaDup.S3 bucket ''
org.gnome.DejaDup.S3 folder 'computername'
org.gnome.DejaDup.S3 id ''
org.gnome.DejaDup.U1 folder '/deja-dup/computername'

So I thought, maybe there's some confusion about the storage type or path.
So I defined once more the backup-path with the USB-Drive online an tried to backup once more.

This backup failed, too.

Checking the new file
/tmp/deja-dup.gsettings
No difference compared to the first one.

The original message is in German:
Datensicherung fehlgeschlagen
Nicht genügend freier Speicherplatz

4.
The file
 DEJA_DUP_DEBUG=1 deja-dup --backup | tail -n 1000 > /tmp/deja-dup.log
is attached but has been shortened.

Thank you.

Best regards

Michael