The way to fix this problem is to eliminate TA relationships that are considered duplicates by BBEC. In BBEC you cannot have multiples of the same relationship type between the same two accounts, even if they have different date ranges.  In TA, you can have multiples so long as only one is active.

More specifically - what happens is that it’s trying to sync 2 records for the transaction, one for each of the duplicate relationships and this can cause two types of problems:

1) The first row is processed successfully, clearing the error row, but the second one is invalid and is causing an error, then can’t find the error row to update because it was just cleared by the first record syncing successfully.
 
2)  Sync tries to insert an error twice for the same record for the record, as a result of the duplicate relationship making the record return twice.

If this error is returned in the sync log, please create a support request at www.blackbaud.com/support providing the full text of the error message and referencing this solution.