Comment by tracker1

Likely a unique index... duplicate insert on a primary or 1:! foreign key. I am currently shimming out a process that will add a trackingid for a job service, and just had my method stub retorn Guid.Empty... second time I ran my local test it blew up on the duplicate key... then I switched it to null, then it blew up again... I neglected to exclude null from the unique index on the foreign key.

In any case, it's easy enough to do. I mostly use UUDv7, COMB or NEWSEQUENTIALID ids myself though.