Khutbah Ilhamyiya has no error. When I say this I refer to the revelation part. Nor has anyone spotted an error in the khutba other than a typo of location. It seems as if the typo came from the writer as its clear what Ahmad(as) is saying. Its possible it was a typo or its possible he had forgotten as Prophets have forgotten many times. In reality when we see the allegation they try saying its revelation not knowing that this was not even revelation rather the khutba started way after. Ahmad(as)’s khutba ilhamiya is not entirely revelation until the khutba actually starts which the anti Ahmadis use to deceive people. Might again be an error in the print press as its clear what Ahmad(as) meant.
Hadhrat Adam(as)’s incident of forgetting mentioned in Qur’an:
And verily, We had made a covenant with Adam beforehand, but he forgot, and We found in him no determination to disobey.(Chapter 20 verse 116)
An incident of Moses(as) forgetting in the Qur’an:
But when they reached the place where the two seas met, they forgot their fish, and it made its way into the sea going away swiftly. And when they had gone further, he said to his young companion: ‘Bring us our morning meal. Surely, we have suffered much fatigue on account of this journey of ours.’(Chapter 18 verse 62-63)
Holy Prophet Muhammad(saw) could forget according to the Qur’an and has made mistakes:
We shall teach thee the Qur’an, and thou shalt forget it not, Except as Allah wills. Surely, He knows what is open and what is hidden.(Chapter 87 verses 7-8)
He frowned and turned aside, Because there came to him the blind man. And what makes thee know that he may be seeking to purify himself, Or he may take heed and the Reminder may benefit him? As for him who is disdainfully indifferent. Unto him thou dost pay attention,(Chapter 80 verse 2-7)
Another incident from the life of the Prophet(saw) in Qur’an:
O Prophet! why dost thou forbid thyself that which Allah has made lawful to thee, seeking the pleasure of thy wives? And Allah is Most Forgiving, Merciful.(Chapter 66 verse 2)
Now let us go to the Ahadith and see some mistakes in the lifetime of the Holy Prophet Muhammad(Saw). In fact there is an entire book in Sahih Bukhari that is named after forgetfulness in prayer. Here is one example:
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، حَدَّثَنَا يَزِيدُ بْنُ إِبْرَاهِيمَ، عَنْ مُحَمَّدٍ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ صَلَّى النَّبِيُّ صلى الله عليه وسلم إِحْدَى صَلاَتَىِ الْعَشِيِّ ـ قَالَ مُحَمَّدٌ وَأَكْثَرُ ظَنِّي الْعَصْرَ ـ رَكْعَتَيْنِ ثُمَّ سَلَّمَ ثُمَّ قَامَ إِلَى خَشَبَةٍ فِي مُقَدَّمِ الْمَسْجِدِ فَوَضَعَ يَدَهُ عَلَيْهَا وَفِيهِمْ أَبُو بَكْرٍ وَعُمَرُ ـ رضى الله عنهما ـ فَهَابَا أَنْ يُكَلِّمَاهُ وَخَرَجَ سَرَعَانُ النَّاسِ فَقَالُوا أَقَصُرَتِ الصَّلاَةُ وَرَجُلٌ يَدْعُوهُ النَّبِيُّ صلى الله عليه وسلم ذُو الْيَدَيْنِ فَقَالَ أَنَسِيتَ أَمْ قَصُرَتْ فَقَالَ “ لَمْ أَنْسَ وَلَمْ تُقْصَرْ ”. قَالَ بَلَى قَدْ نَسِيتَ. فَصَلَّى رَكْعَتَيْنِ ثُمَّ سَلَّمَ ثُمَّ كَبَّرَ فَسَجَدَ مِثْلَ سُجُودِهِ أَوْ أَطْوَلَ، ثُمَّ رَفَعَ رَأْسَهُ فَكَبَّرَ، ثُمَّ وَضَعَ رَأْسَهُ فَكَبَّرَ فَسَجَدَ مِثْلَ سُجُودِهِ أَوْ أَطْوَلَ، ثُمَّ رَفَعَ رَأْسَهُ وَكَبَّرَ.
Narrated Abu Huraira:
The Prophet (ﷺ) offered one of the evening prayers (the sub-narrator Muhammad said, “I think that it was most probably the `Asr prayer”) and he finished it after offering two rak`at only. He then stood near a price of wood in front of the Mosque and put his hand over it. Abu Bakr and `Umar were amongst those who were present, but they dared not talk to him about that (because of excessive respect for him), and those who were in a hurry went out. They said, “Has the prayer been reduced?” A man who was called Dhul-Yadain by the Prophet (ﷺ) said (to the Prophet), “Has the prayer been reduced or have you forgotten?” He said, “Neither have I forgotten, nor has the prayer been reduced.” He said, “Certainly you have forgotten.” So the Prophet (ﷺ) offered two more rak`at and performed Taslim and then said Takbir and performed a prostration of Sahu like his ordinary prostration or a bit longer and then raised his head and said Takbir and then put his head down and performed a prostration like his ordinary prostration or a bit longer, and then raised his head and said Takbir.(Sahih Bukhari Volume 2, Book 22, Hadith #321)
Here is another example:
حَدَّثَنَا أَحْمَدُ بْنُ أَبِي رَجَاءٍ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ سَمِعَ رَسُولُ اللَّهِ صلى الله عليه وسلم رَجُلاً يَقْرَأُ فِي سُورَةٍ بِاللَّيْلِ فَقَالَ “ يَرْحَمُهُ اللَّهُ لَقَدْ أَذْكَرَنِي كَذَا وَكَذَا آيَةً كُنْتُ أُنْسِيتُهَا مِنْ سُورَةِ كَذَا وَكَذَا ”.
Allah’s Messenger (ﷺ) heard a man reciting the Qur’an at night, and said, “May Allah bestow His Mercy on him, as he has reminded me of such-and-such Verses of such-and-such Suras, which I was caused to forget.(Volume 6, Book 61, Hadtih #558)
The Prophet(saw) did not forget the Qur’an when it was being revealed this was much later showing forgetfulness is normal.