I just did a kernel upgrade on the server and after making sure that the IPs and services were working properly I tried to backup a domain through the web interface and got this error:
Plesk Backup Error: Specified file is not accessible
I know that the location for Plesk back up files are located in /var/lib/psa/dumps
The owner was correct, psaadmin:psaadmin. Then I noticed that the tmp directories permissions were set to 700, so after running:
chmod 711 /var/lib/psa/dumps/tmp
I was able to backup through the web interface.