Do you have a tight connection, and is it legal? You need to make sure you have the minimum layover time needed to catch your connecting flight. If it is less time than the minimum, it is considered an illegal, or hot connection (essentially, the airline doesn't owe you anything if you miss your connecting flight). I've compiled a list of minimum layover times required to catch connecting flights at major airports around the world.
Airports - Amsterdam to Dallas
Airports - Denver to London
Airports - Los Angeles to Miami
* There is a disclaimer here in that not all airlines adhere to the exact same minimum connection times, so these times should be used as a guideline only.