I also get this: <p>An exception occurred: Cannot save file data/xengallery/dummy/dummy.jpg in /var/www/clients/client0/web17/web/library/XenGallery/Helper/Image.php on line 1022
The backup was complete - all files and directories are intact. SQL was completely backed up. It may be to do with permissions on the folders? All members, forums, messages are intact.
In order to use that, you must have a valid .htaccess file in place in the installation root and the relevant server configuration.
If the .htaccess file is missing you can rename the htaccess.txt file to .htaccess which may resolve it.
If it doesn't you will need to contact your host to have the server configured correctly.
In the meantime, to restore functionality, you can disable Friendly URLs in the ACP.