I also have this error when I run a remote backup with Innobackupex, and the result is that the xtrabackup_log is missing:
One the box the backup is run from:
110713 13:54:13 innobackupex: Finished backing up .frm, .MRG, .MYD, .MYI, .TRG, .TRN, .ARM, .ARZ, .CSV, .CSM and .opt files
innobackupex: Resuming ibbackup
xtrabackup: The latest check point (for incremental): ‘3497781933050’
log scanned up to (3498117720317)
xtrabackup: Transaction log of lsn (3492260936252) to (3498117720317) was copied.
innobackupex: Error: mysql child process has died: ERROR 2006 (HY000) at line 15: MySQL server has gone away
while waiting for reply to MySQL request: ‘UNLOCK TABLES;’ at /usr/bin/innobackupex line 336.
On the box that backup is made to:
total 215050336
-rw-r–r-- 1 root root 353 2011-07-13 13:50 backup-my.cnf
drwxr-xr-x 2 root root 4096 2011-07-13 19:04 gearman
-rw-r----- 1 root root 220211445760 2011-07-13 13:48 ibdata1
drwxr-xr-x 2 root root 20480 2011-07-13 19:05 mail
drwxr-xr-x 2 root root 20480 2011-07-13 19:05 mail_test
drwxr-xr-x 2 root root 4096 2011-07-13 19:05 mysql
drwxr-xr-x 2 root root 4096 2011-07-13 19:05 weblogs
-rw-r–r-- 1 root root 28 2011-07-13 19:04 xtrabackup_binlog_info
-rw-r–r-- 1 root root 77 2011-07-13 19:04 xtrabackup_slave_info
No xtrabackup_logfile is present due to InnoBackupex error above causing the backup to fail.