Marsi dee, basically singing national anthem of any country is haram according to Islamic beliefs. I wonder why it is being sung in Pakistan although its an Islamic/muslim nation. So basically it may be their belief which stops them to sing national song of their nation. Secondly the song is in Sanskrit and its translation is disputed. Some says that Vande Matram means I pray my Madre watan, some says that It stand for Tasleemat to madre watan. Muslims go for first translation which stands for praying their mother land which goes against Islamic belief. Hence this fatwa.