this is my log file:
flexbackup version 1.1.7 (
http://flexbackup.sourceforge.net)
/etc/flexbackup.conf syntax OK
|------------------------------------------------------------
| Checking 'buffer' on this machine... Ok  Checking /bin/sh on this 
|machine... bash2
|------------------------------------------------------------
| Trying "mt defblksize" instead of "mt setblk"
| Doing level 0 backup of set all using dump  All sets = full (1 tapes)  
|Rewinding & erasing tape...
| Creating index key 200406261316
| Backup set full (/ /boot)
| Tape #0
|------------------------------------------------------------
At block 21.
|------------------------------------------------------------
| File number 1, tape index 200406261316  Backup of: /
| NOTE: $exclude_expr is ignored for type=dump  Date of this level 0 
|backup: Sat Jun 26 13:16:30 2004  Date of last level 0 backup: the 
|epoch
|------------------------------------------------------------
| dump -0 -b 10 -a -f - / | gzip -4 | buffer -m 3m -s 10k -u 100 -t -p 75
|   -B -o "/dev/nst0"
|------------------------------------------------------------
  DUMP: Date of this level 0 dump: Sat Jun 26 13:16:30 2004
  DUMP: Dumping /dev/hda3 (/) to standard output
  DUMP: Added inode 8 to exclude list (journal inode)
  DUMP: Added inode 7 to exclude list (resize inode)
  DUMP: Label: /
  DUMP: mapping (Pass I) [regular files]
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 11370999 tape blocks.
  DUMP: Volume 1 started with block 1 at: Sat Jun 26 13:17:19 2004
  DUMP: dumping (Pass III) [directories]
  DUMP: dumping (Pass IV) [regular files] buffer (writer): write of data failed: Input/output error
bytes to write=10240, bytes written=-1, total written      23160K
  DUMP: Broken pipe
  DUMP: The ENTIRE dump is aborted.
ERROR from backup, exiting
offending command(s):
dump -0 -b 10 -a -f - / | gzip -4 | buffer -m 3m -s 10k -u 100 -t -p 75 -B -o "/dev/nst0"
Backup terminated: backup failed - status: 256