Backup unsuccessful

I've just installed nssbackup 0.2.0 from tar, with Ubuntu Lucid Lynx.
With the default profile (see first attachment of nssbackup.conf), I tried a backup on an external HDD.
This practice worked perfectly with previous Nssbackup versions.

After a while (2 tar files of 3.8 GB and one of 3.6) the nssbackup stops giving an error (Command 'env' failed):

NSSBackup 'Default Profile' Logger

==============

2010-06-02 20:46:47,684 - ERROR: Command 'env' failed.
/bin/tar: Removing leading `/' from member names
/bin/tar: /home/paolo/.cache/syncevolution/ovi-2010-06-01-18-56-1/status.ini: Warning: Cannot stat: No such file or directory
/bin/tar: /home/paolo/.cache/syncevolution/ovi-2010-06-01-18-56-1/status.ini: Warning: Cannot stat: No such file or directory
/bin/tar: /home/paolo/.cache/syncevolution/ovi-2010-06-01-18-56-1/syncevolution-log.html: Warning: Cannot stat: No such file or directory
/bin/tar: /home/paolo/.cache/syncevolution/ovi-2010-06-01-18-56-1/syncevolution-log.html: Warning: Cannot stat: No such file or directory
/bin/tar: /var/log/kern.log: file changed as we read it
/bin/tar: /var/log/messages: file changed as we read it
 (exit code: 1)
2010-06-02 20:46:47,699 - ERROR: An error occured during the backup:
Command 'env' failed.
Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/nssbackup/nssbackupd.py", line 218, in run
    self.__bm.makeBackup()
  File "/usr/lib/python2.6/dist-packages/nssbackup/managers/BackupManager.py", line 374, in makeBackup
    self.__actualSnapshot.commit()
  File "/usr/lib/python2.6/dist-packages/nssbackup/util/Snapshot.py", line 393, in commit
    self.__makebackup()
  File "/usr/lib/python2.6/dist-packages/nssbackup/util/Snapshot.py", line 618, in __makebackup
    TAR.makeTarFullBackup(self)
  File "/usr/lib/python2.6/dist-packages/nssbackup/util/tar.py", line 350, in makeTarFullBackup
    __finish_tar(retVal, outStr, errStr)
  File "/usr/lib/python2.6/dist-packages/nssbackup/util/tar.py", line 394, in __finish_tar
    raise SBException(_errmsg)
SBException: Command 'env' failed.

Thanks for yr help

Paolo