error

<?xml version="1.0" encoding="UTF-8"?>
<nifty xmlns="http://nifty-gui.sourceforge.net/nifty-1.3.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://nifty-gui.sourceforge.net/nifty-1.3.xsd http://nifty-gui.sourceforge.net/nifty-1.3.xsd">

  <useControls filename="nifty-default-controls.xml" />
  <useStyles filename="nifty-default-styles.xml" />
    <screen id="start">
        <layer id="layer1" backgroundColor="#000f">



        </layer>

        <layer id="foreground" backgroundColor="#0000" childLayout="vertical">

            <panel id="top_spacer" height="25%" width="100%" backgroundColor="#0000" childlayout="center" align="center">
            </panel>


            <panel id="top_panel" height="25%" width="100%" backgroundColor="#f008" childlayout="center" align="center">
                <!--  Custom code here -->

                <control name="button" label="Start" id="StartButton" align="center" valign="center">
                </control>

            </panel>


            <panel id="bottom_panel" height="25%" width="100%" backgroundColor="#a008" childlayout="center" align="center">
                <!--  Custom code here  -->


            </panel>

        </layer>

    </screen>

</nifty>