On Ubuntu 11.10, Sun Java 6 Update 29, when trying to backup any file or directory to SFTP, the following exception occurs and the backup aborts:
12-01-25 00:48 - INFO - Flushing /tmp/java/ftpout0 to bup/storage_1921591493/120125_data/transaction/00000000000/content
12-01-25 00:48 - INFO - Flushing /tmp/java/ftpout0 to bup/storage_1921591493/120125_data/hash
12-01-25 00:48 - INFO - Flush...
2012-01-24 15:53:29 PST in Areca Backup