Resolution
Plesk 7.5 and 8.0 versions use different backup formats, so dump that was made using Plesk 7.5 Backup Utilities cannot be restored on Plesk 8.0.
Since Plesk 8.1.1 support for the Plesk 7.5.4 old format backup files is available. With help of 'backup-convert' utility Plesk 7.5.4 dump file can be converted to the new Plesk 8 format. The utility can be found at $PRODUCT_ROOT/bin/backup-convert in Plesk 8.1.1 installation (psa-backup-manager package should be installed).
To convert Plesk 7.5 backup to Plesk 8.0 format use the command like below:
/usr/local/psa/bin/backup-convert convert --output OUTPUT_8.0_DUMP SOURCE_7.5_DUMP
Additional information
If you get the following error during the backup converting:Unexpected XSLT element 'param'.
runtime error: file /usr/local/psa/admin/share/backup_convert/backup-convert.xsl line 283 element param
Unexpected XSLT element 'param'.
runtime error: file /usr/local/psa/admin/share/backup_convert/backup-convert.xsl line 286 element choose
Variable 'no_name' has not been declared.
Please upgrade Plesk to the latest 8.2 version where this problem with backup-convert had been fixed.