Once you had imported SAP DB Version 7.4, you were not able to start the INPLACE migration because no preparations had been made in the original database version for migration.
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1. Import the original database version again.
2. Switch the database instance to ONLINE mode.
3. Shut down the database instance.
4. Run the Database Manager CLI command migrate in a utility session while the database is in ADMIN mode.
This deletes data that is no longer support in Version 7.4.
5. Import Version 7.4 again and restart the INPLACE migration.