Hello Igor,
thanks for your answer.
I tried: # ln -s /var/lib/psa/tmp /usr/local/psa/PMM/tmp and made a backup manually, but the error stays the same.
Again: <description>Failed to pack files 11062013__domainname_mn_1306111329 in /var/lib/psa/dumps/resellers/xy/clients/xy/domains/domainname [...