Nevermind. The error is gone now.In "Public class Program", I have "static Microsoft.SPOT.Hardware.PWM _servo;".
In "public static void Main()", I have "_servo = new Microsoft.SPOT.Hardware.PWM(PWMChannels.PWM_PIN_D10, 20000, 1500, PWM.ScaleFactor.Microseconds, false);"
In "static void button_OnInterrupt", I have "_servo.duration = 1500;". Now it's complaining about "duration".
Error message "Microsoft.SPOT.Hardware.PWM does not contain a definition for duration."
Thanks!