Caught exception: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'node-576-0-0-und' for key 'PRIMARY'

I'm migrating a site from 6 to 7, and have run through the steps many times working out the bugs, and node convert has never been an issue. I create the template, add it as an action, then update the admin view. I have not run through the entire process from the start for about 6 weeks, and now all of a sudden I'm getting this, and the nodes don't convert...at least the process doesn't complete. The fields get migrated, but the bundle type is not updated and the old field data is not removed.

Caught exception: SQLSTATE[23000]: Caught exception: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'node-576-0-0-und' for key 'PRIMARY': 1062 Duplicate entry 'node-576-0-0-und' for key 'PRIMARY'

I can execute the following sql, and then I'll need to cleanup the orphaned field data as a stop gap measure:

UPDATE `d7_table`.`field_data_field_landing_page_body` t1
       JOIN `d7_table`.`node` t2
       ON t1.`entity_id` = t2.`nid`
SET    t2.`type` = 'landing_page';

Thank you!
Sean