BERLIN (AP) — Millions of Europeans who arrived late to work or school Wednesday had a good excuse — an unprecedented lag in the continent's electricity grid that's slowing down some clocks. The problem is caused by a political dispute between Serbia and Kosovo that's sapping a small amount of energy from the local grid, causing a domino effect across the 25-nation network spanning the continent from Portugal to Poland and Greece to Germany. "Since the European system is interconnected ... when there is an imbalance somewhere the frequency slightly drops," said Claire Camus, a spokeswoman for the European Network of Transmission System Operators for Electricity.