Windows Phone NullReferenceException while navigating mystery - windows-phone-8

Question

During page navigatin within my app I display a message in the system tray to the user along with the progress bar to indicate something is going on.
The problem I'm having is during debug I am randomly getting the following error:
{System.NullReferenceException: Object reference not set to an instance of an object.
at ContosoSocial.SetProgressIndicator.<>c__DisplayClass1.<runSystrayMessage>b__0(Object sender, EventArgs args)
at MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)
at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)} System.Exception {System.NullReferenceException}
Stacktrace:
StackTrace " at ContosoSocial.SetProgressIndicator.<>c__DisplayClass1.<runSystrayMessage>b__0(Object sender, EventArgs args)\r\n at MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)\r\n at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)" string
I'm still new to VS2013 and Windows Phone programming so really need a little help here figuring out how to trace and fix this problem?
The error seems to be random, here is an example of the class displaying the system tray message and calling method:
class SetProgressIndicator
{
public void runSystrayMessage(bool isVisible, string text, int length)
{
try
{
SystemTray.ProgressIndicator = new ProgressIndicator();
SystemTray.ProgressIndicator.IsVisible = true;
SystemTray.ProgressIndicator.Text = text;
SystemTray.ProgressIndicator.IsIndeterminate = isVisible;
}
catch (System.InvalidOperationException e)
{
Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
}
DispatcherTimer timer = new DispatcherTimer();
try
{
timer.Interval = TimeSpan.FromMilliseconds(length);
}
catch(ArgumentOutOfRangeException e)
{
Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
}
timer.Tick += (sender, args) =>
{
try
{
SystemTray.ProgressIndicator.IsVisible = false;
}
catch(System.InvalidOperationException e)
{
Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
}
timer.Stop();
};
timer.Start();
}
}
}
Example of a calling method:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
SetProgressIndicator progInd = new SetProgressIndicator();
// Check for full licnece before removing ad's
if (TrialExperienceHelper.LicenseMode == TrialExperienceHelper.LicenseModes.Full)
{
GOTPubCenter10.Visibility = Visibility.Collapsed;
}
// Dispaly message in system tray
if (hasBeenVisited)
{
progInd.runSystrayMessage(true, "Entering house selection menu...", 2500);
}
else
{
progInd.runSystrayMessage(true, "Select house library to enter...", 8000);
hasBeenVisited = true;
}
}
Ideas and suggestions on how to solve the problem appreciated.