The month of Sha^ban is the eighth month of the lunar year in the Islamic calendar and the month immediately preceding the month of Ramadan. For Muslims all around the world, the month of Sha^ban is a special time in which they try to do more good deeds than usual and fast more optional fasts than they do in other months. The Prophet used to fast a lot during this month. It is the habit of the Muslims to celebrate the 15th night of the month of Sha^ban by praying, reciting Qur'an, praising Allah, and making a great deal of supplication to Allah during that night.
Ibn Majah narrated that the Prophet said:
إذا كانت ليلةُ النصفِ من شعبانَ فقوموا ليلَها وصُوموا نهارها
which means: <<Spend the night preceding the 15th day of Sha^ban in acts of obedience, and fast the next day.>>
The acts of obedience meant in this hadith are reciting the Qur'an, making supplication (du^a') to Allah, and praying optional prayers. Although making supplication, in general, is a recommended matter, one needs to be cautious about what he is asking for in his supplication. It must be understood that when one supplicates to Allah (asks Allah for things) one is not asking Allah to change His Will. It is among the essentials of the belief of Muslims that Allah's Will is eternal and does not change. Rather, one would be asking Allah to change one’s situation from a difficult situation to an easier one, from a good situation to a better one, or the like. Knowing this, one needs to be cautious of a supplication which some people recite on the night of the 15th day of Sha^ban. This supplication gives a wrong connotation that Allah changes His Will.
Moreover, it should be noted that this particular supplication was not confirmed from the Prophet nor from ^Umar or Ibn Mas^ud (as explicitly clarified by al-Bayhaqiyy in his book, Al-Qadar).
When reciting that supplication, some people erroneously understand that they are asking Allah to change His Will. This is a dangerous situation. The Will of Allah does not change. This is among the basics of the beliefs of the Muslims. Change is among the very obvious signs that that thing is a creation. Imam Abu Hanifah said: "Change occurs only in the creations."
In conclusion, it is rewardable and recommended to recite the Qur'an, pray, and make supplication during the 15th night of Sha^ban. However, it is blasphemy to make any supplication with the understanding that Allah changes His Will because of this supplication or with the understanding that it is possible that the Will of Allah changes.