During migration D6->D7 I get an error message "Integrity constraint violation"
The error message indicates that your underlying database is having a problem. It looks like you've tried the migration multiple times, and that parts of it were successful previously. What the error message is stating is that you are attempting to insert duplicate records into the database, or at least duplicate keys for an existing record. You need to reset/empty the NEW database prior to running migrate and migrate_d2d to remove the problem.