Error description This error is thrown if by chance the 80-bit random number generated by the ulid word matches 80-bits, and a new ULID is requested within the same millisecond. In this case the specification requires an error to be thrown, because it was not possible to produce two ULIDs, while guarenteeing their sorting order. The best course of action is to retry ULID generation when the next millisecond is on the system clock.