This usually boils down to not having the correct privileges in the user where you are associating the migration repository.
I would drop the user you previously created and start again
Connect to System or SYS and run the following
CREATE USER MIGRATIONREPO IDENTIFIED BY oracle;
ALTER USER MIGRATIONREPO QUOTA UNLIMITED ON USERS;
GRANT CONNECT,RESOURCE,CREATE VIEW ,CREATE MATERIALIZED VIEW to MIGRATIONREPO;
Browse the migration repository connection and just double check that a couple of packages where created.
If it all looks good attempt the migration again.
SQL Developer Team.