The Luminate Online constituent sync fails with the error "The record specified does not exist for this data form". Prior to this, the sync has been performing fine, and no changes to settings have been made.
This occurs when there is a constituent in the export results for the constituent sync that wasn't in the constituent table. When this occurred, the user had the sync only process 50 constituents at a time, so between when time when the export pulled the constituent to be synced, and before the constituent was actually synced, it was merged into another constituent and deleted.
The solution is to have the user re-run the constituent sync with a seed date of the the last time the Constituent sync finished successfully. That way it regenerates the list of constituents, minus any that no longer exist. After this, the Constituent Sync works correctly.
Steps to Duplicate
Run the Constituent Sync between CRM and Luminate Online.