A first chance exception of type 'System.InvalidOperationException' occurred in Microsoft.SPOT.Hardware.dll

Hi

I am trying to get a servo working I copied this code from the internet when I run it, it fails with the following error

A first chance exception of type 'System.InvalidOperationException' occurred in Microsoft.SPOT.Hardware.dll

Any help will be appreciated

Thanks in advance

Graham

Attached is the code I am using on a netduino plus2 version 4.2.2

program.cs

using System.Threading;

using SecretLabs.NETMF.Hardware.Netduino;

using Microsoft.SPOT;

namespace MinelectricsV2

{

public class Program

{

static Servo[] servos = new Servo[4];

public static void Main()

{

//Netduino only has four PWM pins: GPIO_PIN_D5, 6, 9, and 10

servos[0] = new Servo(Pins.GPIO_PIN_D5);

servos[1] = new Servo(Pins.GPIO_PIN_D6);

servos[2] = new Servo(Pins.GPIO_PIN_D9);

servos[3] = new Servo(Pins.GPIO_PIN_D10);

while (true)

{

MoveServos(0);

MoveServos(90);

MoveServos(180);

}

}

private static void MoveServos(uint angle)

{

for (int i = 0; i < servos.Length; i++)

{

servos[i].Angle = angle;

}

Thread.Sleep(2000);

}

}

}

class.cs

using Microsoft.SPOT.Hardware;

using SecretLabs.NETMF.Hardware;

namespace MinelectricsV2

{

public class Servo

{

static PWM servo;

public Servo(Cpu.Pin pin)

{

servo = new PWM(pin);

servo.SetDutyCycle(dutyCycle: 0);

}

private uint _angle = 0;

public uint Angle

{

get

{

return _angle;

}

set

{

const uint degreeMin = 0;

const uint degreeMax = 180;

const uint durationMin = 500; // 480

const uint durationMax = 2300; // 2450

_angle = value;

if (_angle < degreeMin) _angle = degreeMin;

if (_angle > degreeMax) _angle = degreeMax;

uint dur = (_angle - degreeMin) * (durationMax - durationMin) / (degreeMax - degreeMin) + durationMin;

servo.SetPulse(period: 20000, duration: dur);

}

}

}

}