About 50 Anglican clergymen, who are not in communion with the Catholic Church, took part in religious services at the highest-ranking papal basilica in Rome on Tuesday, April 18. The Vatican later released a statement of regret, attributing the incident to a failure in communication.

The clergymen, who were accompanied by Bishop Jonathan Baker of the Church of England, are part of the Anglican Communion, which broke away from the Catholic Church in 1534 amid King Henry VIII’s frustration that he could not receive an annulment for his marriage. The Catholic Church does not consider Anglican holy orders valid and does not recognize Anglican orders as valid, which means they cannot validly celebrate Mass.

The Anglican service was celebrated at the Archbasilica of St. John Lateran in Rome, which is the oldest basilica in Rome and the official seat of the bishop of Rome, the pope.

In a statement issued Thursday, Bishop Guerino Di Tora, who serves as the vicar of the archpriest of the Lateran Basilica, said the incident was the result of a “failure in communication” and that he “expresses deep regret for what happened.”

The statement said that “a group of about 50 priests, accompanied by their bishop, all belonging to the Anglican Communion, celebrated on the high altar of the cathedral of Rome in contravention of the canonical norms. Di Tora also explained that the regrettable episode was caused by a failure in communication.”

Pope Francis met with Baker and the other clergymen on Wednesday morning, but it’s unclear how or why they were given authorization to conduct a religious service at the archbasilica.

The Anglican clergy who took part in the service are Anglo-Catholic. Despite the name, the group is in communion with the Anglican Church and not in communion with the Catholic Church. Anglo-Catholics tend to hold more traditional views than the Anglican Church as a whole, such as an opposition to ordaining women.