Unable to move /usr/share/owncloud/3rdparty/aws-sdk stops the update proces

[Zman]

Trying to update from 5.04 (ubuntu 12.10) to 7.02 is NOT possible.

This results in the following message / warnings:
Failed to create backup.
It stops / breaks the update proces!

In the warnings log it shows:
Unable to move /usr/share/owncloud/3rdparty/aws-sdk to /usr/share/owncloud/backup/tmp/3rdparty/aws-sdk

the backup directory is logically linked to backup -> /var/lib/owncloud/backup.

I tried several approaches: changing the ownership and group from root to www-data.
changing the rights to 777 in the backup directory
creating a tmp directory with all rights and even removing 3rdparty.
Nothing works

Please help