Argentina suing Uruguay

#1
I see that Argentina is taking Uruguay to the World Court with regard to the proposed construction of the two pulp mills. I also saw pictures last weekof the three amigos -- Kirchner, Chavez, and Lula -- smiling and clasping hands in Brasilia (occasion was the construction of a new gas pipeline). Are these two events connected at a deeper level? Do Paraguay and Uruguay feel left out of the new Mercosur, where the big boys dominate? Is there some slight animosity between Argentina and Uruguay? Or am I reading too much in disconnected events?