This is probably a reference to the infamous oracle received by Kroisos of Lydia, as related by Herodotos (1.53):

The Lydians who were to bring these gifts to the temples were instructed by Kroisos to inquire of the oracles whether he was to send an army against the Persians and whether he was to add an army of allies. When the Lydians came to the places where they were sent, they presented the offerings, and inquired of the oracles, in these words: "Kroisos, king of Lydia and other nations, believing that here are the only true places of divination among men, endows you with such gifts as your wisdom deserves. And now he asks you whether he is to send an army against the Persians, and whether he is to add an army of allies." Such was their inquiry; and the judgment given to Kroisos by each of the two oracles was the same: namely, that if he should send an army against the Persians he would destroy a great empire.

The result, of course, was that Kroisos was defeated by Kyros the Great, and that Lydia was taken by the Persians; the great empire he destroyed was his own. It seems Alexander of Abonoteichos used this story to excuse himself for predicting a great victory for the Romans against the Marcomanni, when in fact the Romans suffered a defeat.