error when adding a wpf theme to application

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WPF

this is my app.xaml:

<Application x:Class="Hearts.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary Source="Theme.xaml"/>
    </Application.Resources>
</Application>

there isn't a Theme.cs
this is my Theme.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
                    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                    mc:Ignorable="d" 
                    xmlns:d="http://schemas.microsoft.com/expression/blend/2008">

    <!--SHINY BLUE SETTINGS FOR CHARTS-->
    <LinearGradientBrush x:Key="ShinyChartOrange" EndPoint="0.5,1" StartPoint="0.5,0">
        <GradientStop Color="#FFFDDBAE" Offset="0" />
        <GradientStop Color="#FFCE955A" Offset="0.185" />
        <GradientStop Color="#FFAB7547" Offset="0.475" />
<!-- Long code here i got from look at link  -->
</ResourceDictionary >

codeplex wpf themes

and now i have this error:

System.Reflection.TargetInvocationException
Exception has been thrown by the target of an invocation.
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

 
System.InvalidCastException
Unable to cast object of type 'System.Windows.Media.Color' to type 'System.Windows.Media.Brush'.
   at MS.Internal.Text.TextProperties.InitCommon(DependencyObject target)
   at MS.Internal.Text.TextProperties..ctor(FrameworkElement target, Boolean isTypographyDefaultValue)
   at System.Windows.Controls.TextBlock.GetLineProperties()
   at System.Windows.Controls.TextBlock.EnsureTextBlockCache()
   at System.Windows.Controls.TextBlock.MeasureOverride(Size constraint)

if full stack is required just ask.

what is the problem?

Thanks,
Gabriel Sas