Permitted development rules- Scotland

[ericardlussa]

I have rebuilt a totally dilapidated outhouse/storage shed (of corrugated iron construction) connected to original dwelling house, on a smaller footprint than original but now of traditional materials, under 30 sq metres, and have received letter from planners stating that planning permission is required, I had thought this would come within permitted development, is this not the case?
Original dwelling house around 60 sq m and original outhouse around 35 sq m.