Synology support is useless as you can see in this thread alone there is not a single reply posted by a technician at Synology as a resolution to this problem. They are only interested in selling, not after market support. I am having this same problem too but don't have don't have the technical prowess to deal with cryptic log messages. I get this when I try to rsync my QNAP NAS to Synology (DS1515+) as a backup.
rsync: delete_file: unlink(Mac 170914a/Grammarian Pro2 X v2.0.4/@eaDir/GrammarianPRO2X204.dmg@SynoEAStream) failed: Permission denied (13)
The message is caused by attempting by the Synology in response to attempting to backup shares on the QNAP to the same shares on the Synology.
I am gradually switching to QNAP. Not only are their NASes more feature-rich such as direct HDMI and thunderbolt 3 connectivity and dual functionality as a DAS / NAS, their support staff are superb. My second NAS, which is the Synology causing this problem to occur and without any resolution, will soon be sold. I intend to invest in a second QNAP as backup NAS and other functionality.
For those needing a resolution to this problem, I suggest submitting a support ticket to Synology's help desk directly. There might be a quicker resolution to this problem versus expecting some Synology technician to address the issue here on a forum discussion. My 2-cents worth. (top of page)
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