mohammad2d:
so I tried to wire the servo to Ardunio output directly without the shield and it runs smoothly ... I did noticed some voltage drop on the Power On LED on the board when the servo reaches it's maximum angle though.
Does the sensor shield have any active electronics? If the servo is causing the voltage to dip it can only get worse if you add any other loads. Try adding a separate power supply for the servos. The sensor shield should allow for that.