Overview:

Error when syncing Affiliations offline:  duplicate value found: External_Id_vod__c duplicates value on record with id.

Root Cause:

There are several ways this error can occur: 

1. A user creates an Affiliation Online, does not sync the changes, and then creates the affiliation again Offline. On the next sync, the rep returns a Duplicate Affiliation error, since it already exists Online. 
2. A User creates an affiliation and syncs the record Online. A different user creates the same affiliation and tries to sync the record Online. The other user receives the Duplicate Affiliation error because the affiliation already exists.
3. The Data team loads affiliations for the reps. A User creates an affiliation Offline that is loaded Online. Since the user did not run the sync, the affiliation does not appear immediately Offline. The user syncs. A Duplicate Affiliation error occurs because it exists online.
4. The user should have edit FLS to the Disable_Trigger_vod__c field on the Affiliations object.

Solution: