adding a resources in window

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WPF

sir ! i have written this code in c# xaml !
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<window x:class="dynamic_resources.MainWindow" xmlns:x="#unknown">
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
Title="Gradient sample" Height="350" Width="525" removed="{DynamicResource windowsBackgrounBrush}"> //warning about this line!
<window.resources>
<sys:string x:key="ComboBoxtitle" xmlns:sys="#unknown">items
<x:arrayextension x:key="ComboBoxItems" type="sys:String">
<sys:string xmlns:sys="#unknown">Item#1
<sys:string xmlns:sys="#unknown">Item#2
<sys:string xmlns:sys="#unknown">Item#3

<lineargradientbrush x:key="windowsBackgroundBrush"> <gradientstop offset="1" color="Gray">
<gradientstop offset="2" color="silver">

<stackpanel margin="10">
<Label Content="{StaticResource ComboBoxtitle}"/>
<combobox itemssource="{StaticResource ComboBoxItems}">



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this is working fine but there is not any gradient effect is not displayed !
it is showing a warning:

Warning 1 The resource "windowsBackgrounBrush" could not be resolved. c:\users\tushar\documents\visual studio 2012\Projects\dynamic_resources\dynamic_resources\MainWindow.xaml 5 58 dynamic_resources
.