did you check this code?
$url='http://negarjoonam.blogfa.com/rss.aspx';
$doc = new DOMDocument();
$doc->load($url);
please check this simple code to see if any error is returned.
i tried to open the same link using fopen. this is the result:
<html>
<head>
<title>Server Error</title>
<meta http-equiv="Content-Language">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="robots" content="noindex">
</head>
<body>
<div style="HEIGHT:25%"></div>
<div align="center">
<div dir="rtl" align="center" style="line-height:150%;BORDER-RIGHT: #cccccc 1px solid; BORDER-TOP: #cccccc 1px solid; MARGIN-TOP: 32px; PADDING-BOTTOM: 24px; BORDER-LEFT: #cccccc 1px solid; COLOR: #333333; PADDING-TOP: 24px; BORDER-BOTTOM: #cccccc 1px solid; ; BACKGROUND-COLOR: #ffffcc; FONT-SIZE: 8pt; WIDTH: 83%; FONT-FAMILY: Tahoma">
<p><b><span style="color:#800000;font-family:tahoma;font-size:8pt;font-weight:600" >there is a problem in running the script requested or server is being updated. please reapet your request at a later time</p>
</div>
</div>
</body>
</html>
in the same time i tested the link using http://feedvalidator.org . it was loaded without any problem. what's wrong i don't know?