According to the 1917 Catholic Encyclopedia, the Liber Diurnus Romanorum Pontificum is:
A miscellaneous collection of ecclesiastical formularies used in the papal chancery until the eleventh century. It contains models of the important official documents usually prepared by the chancery; particularly of letters and official documents in connexion with the death, the election, and the consecration of the pope; the installation of newly elected bishops, especially of the suburbicarian bishops; also models for the profession of faith, the conferring of the pallium on archbishops, for the granting of privileges and dispensations, the founding of monasteries, the confirmation of acts by which the Church acquired property , the establishment of private chapels, and in general for all the many decrees called for by the extensive papal administration. The collection opens with the superscriptions and closing formulæ used in writing to the emperor and empress at Constantinople, the Patricius, the Exarch and the Bishop of Ravenna, a king, a consul; to patriarchs, metropolitans, priests, and other clerics. The collection is important both for the history of law and for church history, particularly for the history of the Roman Church. The formularies and models set down are taken from earlier papal documents, especially those of Gelasius I (492-6) and Gregory I (590-604).
The Liber Diurnus was subscribed to by popes until the 11th century, and it explicitly condemned Honorius on theological grounds, as did the 7th and 8th ecumenical councils. As Robert Sungenis noted:
And finally, the 7th and 8th ecumenical councils condemned Honorius, and the Liber Diurnus continued to condemn Honorius until the 11th century, so that all people of all times would know that unless the Pope claims to be speaking authoritatively from his Petrine office; defines, not merely hypothesizes, on a matter of faith or morals, and binds all Christians of all times to his unchangeable decree, then there is no infallibility.
Pope Gregory VII, who reigned from 1073-1085, and who subscribed to the Liber Diurnus that condemned Honorius, said: "The Holy Roman Church through blessed Peter, has been understood by the holy Fathers from the earliest origins of the faith as mother of all the churches, and so shall she ever be considered to the end, in which it is clear that no heretic ever presided nor we trust will any ever be put in charge, for the Lord Jesus said, ‘I have prayed for thee Peter that thy faith may not fail." (Migne, PL 148, 573). (Robert Sungenis, Debate on Papal Infallibility, section III [no longer online, but a copy is on my files--if anyone wants it, I will email it to them upon request])
The Catholic Encyclopedia (1917), in the aforementioned entry for the Liber Diurnus, admitted that it “recognized the Sixth General Council and its anathemas against Pope Honorius for his (alleged) Monothelism.”
Liber Diurnus Romanorum Pontificum, in the 1480 edition prepared by Joannis Garnerii, on p. 41 reads:
Autores vero novi haeretici dogmatis Sergium, Pyrrhum, Paulum, & Petrum Constantinopolitanos, una cum Honorio, qui pravis eorum affertionibus fomentum impendit . . .
An English translation of the underlined Latin is:
The authors of the new practice of heretical teaching, however, Sergius, Pyrrhus, Paul, and Peter of Constantinople, together with Honorius . . .
Here is an image of the relevant page:
I raise this as it shows that the common apologetic that Honorius was not condemned for theological error, and was instead condemned merely for not being as vigilant against Monothelitism (e.g., Karl Keating, Catholicism and Fundamentalism; Patrick Madrid, Pope Fiction; Tim Staples [debate vs. James White on Papal Infallibility]; John Lane [Sedevacantist], etc) is without historical merit. A better defense of Honorius vis-à-vis Papal Infallibility as defined in 1870 at Vatican I is the proposal of John Chapman who argued that Honorius was materially a heretic, but not formally so. For a book-length discussion, see:
John Chapman, The Condemnation of Pope Honorius (Catholic Truth Society, 1907)
While I disagree with papal infallibility, I do believe that this approach is sounder, and many Catholics have followed Chapman’s proposal (e.g., B.C. Butler; Robert Sungenis; John Salza; Robert Siscoe; Steve Ray; Dave Palm; Trent Horn).