WP8后台代理-代码在代理外部执行良好，在代理内部失败

我创建了一个后台代理来更新我的活动磁贴。代理调度和执行得很好，但是代理执行的代码成了问题——它只是无法完全执行，没有提供任何错误。据我所知，我没有使用任何受限的api，除非Cimbalino工具包在某种程度上提供了一个问题，即使我使用的是NuGet的特定于后台代理的版本。

代码似乎停止执行时，RenderText()和RenderTextWide()失败运行。没有提供错误。同样的代码在前台应用程序中运行时效果非常好。

using System;
using System.Windows;
using Microsoft.Phone.Scheduler;
using Microsoft.Phone.Shell;
using Microsoft.Phone.Info;
using Cimbalino.Phone.Toolkit;
using System.Linq;
using System.Windows.Media.Imaging;
using System.Windows.Media;
using System.Windows.Controls;
using System.IO.IsolatedStorage;
using Cimbalino.Phone.Toolkit.Extensions;
namespace ScheduledTaskAgent1
{
    public class ScheduledAgent : ScheduledTaskAgent
    {
        private static volatile bool _classInitialized;
        public ScheduledAgent()
        {
            if (!_classInitialized)
            {
                _classInitialized = true;
                // Subscribe to the managed exception handler
                Deployment.Current.Dispatcher.BeginInvoke(delegate
                {
                    Application.Current.UnhandledException += ScheduledAgent_UnhandledException;
                });
            }
        }
        /// Code to execute on Unhandled Exceptions
        private void ScheduledAgent_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
        {
            if (System.Diagnostics.Debugger.IsAttached)
            {
                System.Diagnostics.Debugger.Break();
            }
        }
        //Method to create normal tile image
        private static void RenderText(string currproperty)
        {
            WriteableBitmap b = new WriteableBitmap(336, 336);
            var canvas = new Grid();
            canvas.Width = b.PixelWidth;
            canvas.Height = b.PixelHeight;
            var background = new Canvas();
            background.Height = b.PixelHeight;
            background.Width = b.PixelWidth;
            SolidColorBrush backColor = new SolidColorBrush(Colors.Transparent);
            background.Background = backColor;
            TextBlock currtemp = new TextBlock();
            currtemp.FontSize = 100;
            currtemp.FontFamily = new FontFamily("Segoe UI Light");
            currtemp.FontWeight = FontWeights.Bold;
            currtemp.Foreground = new SolidColorBrush(Colors.White);
            currtemp.Text = currproperty;
            currtemp.Margin = new Thickness(20, 10, 0, 0);
            currtemp.Width = b.PixelWidth - currtemp.Margin.Left * 2;
            canvas.Children.Add(currtemp);
            b.Render(background, null);
            b.Render(canvas, null);
            b.Invalidate();
            using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (IsolatedStorageFileStream imageStream = new IsolatedStorageFileStream("/Shared/ShellContent/BackBackgroundImage2.png", System.IO.FileMode.Create, isf))
                {
                    b.SavePng(imageStream);
                }
            }
        }
        //Method to create wide tile image
        private static void RenderTextWide(string currproperty)
        {
            WriteableBitmap b = new WriteableBitmap(691, 336);
            var canvas = new Grid();
            canvas.Width = b.PixelWidth;
            canvas.Height = b.PixelHeight;
            var background = new Canvas();
            background.Height = b.PixelHeight;
            background.Width = b.PixelWidth;
            //Created background color as Accent color
            SolidColorBrush backColor = new SolidColorBrush(Colors.Transparent);
            background.Background = backColor;
            TextBlock currtemp = new TextBlock();
            currtemp.FontSize = 100;
            currtemp.FontFamily = new FontFamily("Segoe UI Light");
            currtemp.FontWeight = FontWeights.Bold;
            currtemp.Foreground = new SolidColorBrush(Colors.White);
            currtemp.Text = currproperty;
            currtemp.Margin = new Thickness(20, 10, 0, 0);
            currtemp.Width = b.PixelWidth - currtemp.Margin.Left * 2;
            canvas.Children.Add(currtemp);
            using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (IsolatedStorageFileStream imageStream = new IsolatedStorageFileStream("/Shared/ShellContent/WideBackBackgroundImage2.png", System.IO.FileMode.Create, isf))
                {
                    b.SavePng(imageStream);
                }
            }
        }
        //When task invokes, run the tile update code.
        protected override void OnInvoke(ScheduledTask task)
        {
            ShellTile tile = ShellTile.ActiveTiles.FirstOrDefault();
            if (tile != null)
            {
                FlipTileData flipTile = new FlipTileData();
                flipTile.Title = "";
                flipTile.BackTitle = "Atmosphere";
                RenderText("Test");
                RenderTextWide("Test");
                flipTile.BackBackgroundImage = new Uri("/Assets/NewUI/1.PNG", UriKind.Relative); //Default image for Background Image Medium Tile 336x336 px
                flipTile.BackgroundImage = new Uri(@"isostore:/Shared/ShellContent/BackBackgroundImage2.png", UriKind.Absolute); //Generated image for Back Background 336x336
                flipTile.WideBackBackgroundImage = new Uri("/Assets/NewUI/2.PNG", UriKind.Relative); ////Default image for Background Image Wide Tile 691x336 px
                flipTile.WideBackgroundImage = new Uri(@"isostore:/Shared/ShellContent/WideBackBackgroundImage2.png", UriKind.Absolute);
                tile.Update(flipTile);
                //Tile updated, tell agent operation complete
                NotifyComplete();
            }
        }      
    }
}