As of version 7.7, the catalog data of the database is stored in Unicode. You can therefore upgrade to version 7.7 only if the catalog data of the database to be updated is stored in Unicode. If you want to upgrade a database from version 7.5 or 7.6 to version 7.7 and the database catalog was stored in ASCII, you must migrate the database catalog to Unicode before the upgrade.
For more information, see Upgrade
SAP Note 1007129 (FAQ: DB migration with MaxDB as target)