RN516 Backups to ReadyNAS Pro Fail after Upgrade to Firmware 5.6.1

My incremental backups from my RN516 to my ReadyNAS Pro have been running successfully since Nov, 2014.

On Aug 1, 2016, I updated the firmware on RN516 to 5.6.1 and on Aug 2, 2016, my backups starting failing:

Here's a copy of today's log file (failure):

Backup Job Name: Documents
Backup Job Type: Incremental
Protocol: rsync
Backup Source: [Documents]//
Backup Destination: [remote:rsync]/192.168.1.20::Documents
Backup Start Time: Wed Aug 10 2016 19:58:54
Backup Finish Time: Wed Aug 10 2016 19:58:54
Backup Status: Fail: failure during copy.

Failed to run rsync, return rc 2560 (10)
'rsync' command returns rc=2560

sending incremental file list
rsync: read error: Connection reset by peer (104)
rsync error: error in socket IO (code 10) at io.c(785) [sender=3.1.1]

While I can successfully test the connection to to ReadyNAS Pro, it looks like the Backup is failing quickly when trying to "copy" the files on the RN516.
None of my backup settings have changed since 2014.

Any ideas on what's going on?

Thanks,