回複：請教: "canceled without prejudice" 作何解釋?

Canceled without prejudice means what it says. This is usually used to cancel an existing VISA for a valid reason and not for fraud or misconduct etc. Perhaps the visa had a mistake on it. Perhaps it was a multiple entry, indefinite validity visa which the visa officer was taking out of circulation. Whatever the reason, it carries no harmful effect on your status or your eligibility to apply for a benefit.
There is nothing negative attached to the cancellation.

In the case above post, this means that the J1 visa was cancelled, and then issued a new F1 visa to the applicant for him/her to enter U.S.