Does Allah come down to the first heaven on the night of the fifteenth of Shaban and forgive all the people except two types, namely kaafirs and those engaged in disputes?.
Praise be to Allaah.  
This is mentioned in some hadiths, but there is some scholarly difference of opinion as to the soundness of those hadith. There is no saheeh hadith concerning the virtue of the night of the fifteenth of Shaban.
It was narrated from Abu Moosa al-Ash’ari that the Messenger of Allah (peace and blessings of Allah be upon him) said: “Allah looks down on the night of the fifteenth of Shaban and forgives all his creation except a mushrik or one who harbours hatred against the Muslims.” Narrated by Ibn Maajah, 1390.
The “one who harbours hatred against the Muslims” means one who has enmity towards a Muslim brother.
In al-Zawaa’id it says: Its isnaad is da’eef, because ‘Abd-Allaah ibn Lahee’ah is da’eef (weak) and al-Waleed ibn Muslim is mudallis.
There is also some idtiraab (weakness) in the hadith, as stated by al-Daaraqutni in al-‘Ilal, 6/50, 51. He said: This hadith is not proven.
It was narrated from Mu’aadh ibn Jabal, ‘Aa’ishah, Abu Hurayrah, Abu Tha’labah al-Khushani and others, but the isnaads are not free of some weakness, and some of them are very weak.
Ibn Rajab al-Hanbali said:
Concerning the virtue of the night of the fifteenth of Shaban there are numerous ahaadeeth, concerning which the scholars differed, but most of them classed them as da’eef, and Ibn Hibbaan classed some of them as saheeh.
Allah’s descending to the first heaven does not only happen on the night of the fifteenth of Shaban, rather it is proven in al-Saheehayn and elsewhere that Allah descends to the first heaven every night, in the last third of the night. The night of the fifteenth of Shaban is included in this general meaning.
Hence, when ‘Abd-Allaah ibn al-Mubaarak was asked about the descent of Allah on the night of the fifteenth of Shaban, he said to the one who asked him: “O weak one! The night of the fifteenth?! He descends every night!”
Narrated by Abu ‘Uthmaan al-Saabooni in I’tiqaad Ahl al-Sunnah, no. 92.
Al-‘Aqeeli (may Allaah have mercy on him) said:
With regard to Allah’s descending on the night of the fifteenth of Shaban there are ahaadeeth, which are weak, but the reports that He descends every night are proven and saheeh, so the night of the fifteenth of Shaban is included in that.