XUL / XML Parsing Error: undefined entity <listitem

Does anybody know why this error is poping up ?

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://onsip/content/options/options.css"?>

<!DOCTYPE dialog SYSTEM "chrome://onsip/locale/options.dtd">

<dialog xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        id="onsip-options-dialog"
        title="OnSIP Options"
        buttons="accept, cancel"
        ondialogaccept="onsip.saveOptions()">
  <script src="chrome://onsip/content/onsip.js"/>
  <script src="chrome://onsip/content/preferences.js"/>
  <script src="chrome://onsip/content/options/options.js"/>

  <hbox flex="1">
    <listbox id="onsip-page-list" onselect="onsip.changePage(this)">
        <listitem label="&onsip.options.general.label;" selected="true" value="chrome://onsip/content/options/pages/general.xul" />
    </listbox>
    <vbox flex="1">
      <iframe flex="1" id="onsip-options-if开发者_C百科rame"
              src="chrome://onsip/content/options/pages/general.xul"/>
    </vbox>
  </hbox>
</dialog>

the code is above, please if anybody has wider knowledge in XUL drop a note, would be very thankful. S.

Check if &onsip.options.general.label is present in chrome://onsip/locale/options.dtd. If not define it.

The issue was that the "ru-RU" localization was not there, So to solve this issue I have just made a localization for "RU", though still didn't get how to set a default localization .