XamlParseException: Cannot find a Resource with the Name/Key PhoneBackgroundBrush [Line: 47 Position: 111]

Question

When I first started developing everything was fine but then started up the project for the second time got this error. Since there is an error in the xaml the preview of the design layout never shows so I'm working blindly here.

Did some research, where this individual had the exact problem as me but I tried their solution but it didn't work for me maybe because they were working with Windows Phone 7.1 and Im working with 8. Here's the link: VS Developer Express for Windows Phone new project shows XamlParseException

Any help would be greatly appreciated!

MainPage.xaml:

<phone:PhoneApplicationPage
    x:Class="PetSounds.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">

    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="LayoutRoot" Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
            <TextBlock Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}" Margin="12,0"/>
            <TextBlock Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <Button Name="PlayAudioButton"
                    Height="200"
                    Width="200"
                    HorizontalAlignment="Left"
                    VerticalAlignment="Top"
                    Background="Red"
                    Click="PlayAudioButton_Click_1">Quack</Button>
            <MediaElement x:Name="QuackMediaElement"
                          Source="/Assets/Audio/Animals/Duck.wav"
                          Volume="1"
                          AutoPlay="False"
                          />
        </Grid>
    </Grid>

</phone:PhoneApplicationPage> 

EDIT

Here is the App.Xaml file:

<Application
    x:Class="PetSounds.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone">

    <!--Application Resources-->
    <Application.Resources>
        <local:LocalizedStrings xmlns:local="clr-namespace:PetSounds" x:Key="LocalizedStrings"/>
    </Application.Resources>

    <Application.ApplicationLifetimeObjects>
        <!--Required object that handles lifetime events for the application-->
        <shell:PhoneApplicationService
            Launching="Application_Launching" Closing="Application_Closing"
            Activated="Application_Activated" Deactivated="Application_Deactivated"/>
    </Application.ApplicationLifetimeObjects>

</Application>

If needed let me know and I will post the other files.