DataContext and Command in silverlight when used together is not working

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Silverlight

MVVM

I am using Silverlight 4.0 to implement MVVM architecture, I have got a usercontrol TestMVVM.View.EmployeeView and a view EmployeeList within this usercontrol. EmployeeList contains some textbox and a button. My problem is when I use DataContext on the EmployeeList as given in the code the command on button stops working but if I remove DataContext from EmployeeList the command of button works fine.
Below is the code

<usercontrol x:class="TestMVVM.View.EmployeeView" xmlns:x="#unknown">
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:VM="clr-namespace:TestMVVM.ViewModel"
    xmlns:view="clr-namespace:TestMVVM.View"          
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk" 
    >
    <usercontrol.datacontext>
        <vm:employeelistviewmodel xmlns:vm="#unknown" />
    </usercontrol.datacontext>
    <grid x:name="LayoutRoot" removed="White">
        <grid.rowdefinitions>
            <rowdefinition></rowdefinition>
            <rowdefinition></rowdefinition>
        </grid.rowdefinitions>
        <grid.columndefinitions>
            <columndefinition></columndefinition>
            <columndefinition></columndefinition>
        </grid.columndefinitions>
        <sdk:datagrid autogeneratecolumns="False" height="160" horizontalalignment="Left" name="dataGrid1" verticalalignment="Top" width="105" itemssource="{Binding EmployeeList,Mode=OneTime}" selecteditem="{Binding SelectedEmployee,Mode=TwoWay}" xmlns:sdk="#unknown">
            <sdk:datagrid.columns>
                <sdk:datagridtextcolumn header="Age" binding="{Binding Age,Mode=TwoWay}" canuserreorder="True" canuserresize="True" canusersort="True" width="Auto" />
                <sdk:datagridtextcolumn header="Name" binding="{Binding Name,Mode=TwoWay}" canuserreorder="True" canuserresize="True" canusersort="True" width="Auto" />
            </sdk:datagrid.columns>
        </sdk:datagrid>
        <view:employeelist grid.row="0" grid.column="1" datacontext="{Binding SelectedEmployee}" xmlns:view="#unknown">

        </view:employeelist>


    </grid>
</usercontrol>

//view 2

<usercontrol x:class="TestMVVM.View.EmployeeList" xmlns:x="#unknown">
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    xmlns:VM="clr-namespace:TestMVVM.ViewModel" 
    d:DesignHeight="300" d:DesignWidth="400">
    <grid x:name="LayoutRoot" removed="White">
        <grid.rowdefinitions>
            <rowdefinition height="20"></rowdefinition>
            <rowdefinition height="20"></rowdefinition>
            <rowdefinition height="20"></rowdefinition>
        </grid.rowdefinitions>
        <grid.columndefinitions>
            <columndefinition></columndefinition>
            <columndefinition></columndefinition>
        </grid.columndefinitions>
        <textblock x:name="name" text="Name"></textblock>
        <textbox grid.column="1" x:name="txt_name" text="{Binding Name,Mode=TwoWay}">
        </textbox>
        <textblock grid.row="1" x:name="age" text="Age"></textblock>
        <textbox grid.column="1" grid.row="1" x:name="txt_age" text="{Binding Age,Mode=TwoWay}">
        </textbox>
        <Button x:Name="btn_Add" Grid.Row="3" Content="Add" Command="{Binding Path=testCommand}" ></Button>
    </grid>
</usercontrol>