[Error] When i select backup a domain show the code of the page

[rihemo]

Hi when i try to access to plesk backup utility from any domain always show a code
any help please?

example:

!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>
<link rel="shortcut icon" href="/favicon.ico">
<title>Plesk</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script language="javascript" type="text/javascript" src="/javascript/common.js?plesk_version=psa-8.6.0-86080910.19"></script>
<script language="javascript" type="text/javascript" src="/javascript/main.js?plesk_version=psa-8.6.0-86080910.19"></script>
<script language="javascript" type="text/javascript" src="/javascript/chk.js.php?plesk_version=psa-8.6.0-86080910.19"></script>
<script language="javascript" type="text/javascript" src="/javascript/prototype.js?plesk_version=psa-8.6.0-86080910.19"></script>
<!--[if lt IE 7]><script language="javascript" type="text/javascript" src="/javascript/main.leIE7.fixes.js?plesk_version=psa-8.6.0-86080910.19"></script><![endif]-->



<link rel="stylesheet" type="text/css" href="/skins/longhorn.black/css/general.css">
<link rel="stylesheet" type="text/css" href="/skins/longhorn.black/css/main/custom.css">
<link rel="stylesheet" type="text/css" href="/skins/longhorn.black/css/main/layout.css">
<link rel="stylesheet" type="text/css" href="/skins/longhorn.black/css/main/desktop.css">
<!--[if IE]><link rel="stylesheet" type="text/css" href="/skins/longhorn.black/css/ie.css"><![endif]-->
<link rel="stylesheet" type="text/nonsense" href="/skins/longhorn.black/css/misc.css">