Python 2 - 78 bytes
This short, until rules with exit1 are clarified. Now exits with error if nothing is found
def F(a,s): while len(a): y=a.pop() for x in a: if x+y==s:r=x,y print r This short, until rules with exit1 are clarified. Now exits with error if nothing is found
def F(a,s): while len(a): y=a.pop() for x in a: if x+y==s:r=x,y print r