I was trying to back up a domain, but Plesk was just keep throwing me the following error:
“Unable to create backup session: Specified file is not accessible”
I guess something happened at last Plesk upgrade that broke something. After googling for a solution i found it quickly:
Login with root and issue the following command:
chown -R psaadm:psaadm /var/lib/psa/dumps
That should fix it.