The errors I get are..

Can anyone tell me what is wrong with my code ?

This feed does not validate.

line 48, column 11: XML parsing error: <unknown>:43649:2: mismatched tag [help]

</channel>
^

In addition, interoperability with the widest range of feed readers could be improved by implementing the following recommendations.

Feeds should not be served with the "text/html" media type [help]


line 3, column 0: Undocumented use of atom:link [help]

<atom:link href="http://www.site.com/rss.php" rel="self" type="applic ...

Code:
<?xml version="1.0" encoding="windows-1252" ?>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
<atom:link href="http://www.site.com/rss.php" rel="self" type="application/rss+xml">
<channel>
<ttl>1</ttl>
<title>Welcome to our RSS Feed</title>
<link>http://www.site.com?s=rssimg</link>
<description>RSS Feed</description>
<language>en-us</language>
<pubDate>Mon, 02 Jan 2012 20:53:28 GMT</pubDate>
<lastBuildDate>Mon, 02 Jan 2012 20:53:28 GMT</lastBuildDate>
<generator>OnTheFly</generator>
<image>
 <title>Welcome to our RSS Feed</title>
 <url>http://www.site.com/images/header.png</url>
 <link>http://www.site.com?s=rssimg</link>
 <width>88</width>
 <height>31</height>
</image>
<item>
<![CDATA[
<title>title 4</title>
<guid>http://www.site.com/?v=4&amp;h=r</guid>
<pubDate>Tue, 27 Dec 2011 12:35:51 GMT</pubDate>
]]>
</item>
<item>
<![CDATA[
<title>title 3</title>
<guid>http://www.site.com/?v=3&amp;h=r</guid>
<pubDate>Mon, 26 Dec 2011 19:03:16 GMT</pubDate>
]]>
</item>
<item>
<![CDATA[
<title>title 2</title>
<guid>http://www.site.com/?v=2&amp;h=r</guid>
<pubDate>Mon, 26 Dec 2011 19:03:15 GMT</pubDate>
]]>
</item>
<item>
<![CDATA[
<title>title 1</title>
<guid>http://www.site.com/?v=1&amp;h=r</guid>
<pubDate>Fri, 01 Sep 2006 00:00:00 GMT</pubDate>
]]>
</item>
</channel>
</rss>