The story about Ernst composing an opera for the Baden Opera in 1862 strayed beyond the specialist music press and into English provincial newspapers:
Herr Ernst, whose health continues to be in a melancholy state, has composed a small opera to be produced next season at Baden.
Newcastle Journal, 6/11/1861, p.4
Given Ernst’s state of health, his inexperience as a vocal composer, and the lack of any surviving documents suggesting preparation or composition, it is highly unlikely that Ernst ever entertained the intention of writing such a work. Hugh Macdonald has suggested to me that journalists probably confused Ernst with the French composer Ernest Reyer (1823-1909) whose two-act opera Érostate was performed at Baden in 1862. Ernst was completing his Bb string quartet during this period (his first ambitious new work for many years), and it’s quite possible that he referred to this ironically as ‘an opera’ (i.e. work) thereby engendering or adding to the confusion.