Ages of Doubt
From Halopedia, the Halo wiki
Covenant history
The Age of Doubt was when the Covenant had a crisis finding the Halos. The Covenant then began to doubt the word of the Prophets, due to the fruitlessness in their search for Halo. This Also could have been the time when the Taming Of The Hunters occurred, resulting in the need of a Arbiter.
Note: There could be another Age of Reconciliation following the Age of Doubt.