Originally Posted by NickB

If they wrongly refused to let you board, then this would constitute an involuntary denied boarding under regulation 261/2004, which would entitle you to €600 in compensation.
If your country of destination does indeed require a number of blank pages on the passport and you did not have enough blank pages, then they could legitimately deny you boarding.
The fact that they allowed you to travel the next day would tend, on the face of it, to suggest that the former rather than the latter is true.