RSS Server returned HTTP Error 404: Not Found

Dear all,

I have a wordpress multisite installation into an Ubuntu server. At the present time I’m creating a blog, an everything is working OK with it, but the RSS. It is not working at all.

When checking it through a RSS Validator, it is returning me the following:

This feed does not validate.

Server returned HTTP Error 404: Not Found

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0"
xmlns:content="https://purl.org/rss/1.0/modules/content/"
xmlns:wfw="https://wellformedweb.org/CommentAPI/"
xmlns:dc="https://purl.org/dc/elements/1.1/"
xmlns:atom="https://www.w3.org/2005/Atom"
xmlns:sy="https://purl.org/rss/1.0/modules/syndication/"
xmlns:slash="https://purl.org/rss/1.0/modules/slash/"
>

<channel>
<title>Good Morning Kitty » Page not found</title>
<atom:link href="https://www.goodmorningkitty.com/feed/" rel="self" type="application/rss+xml" />
<link>https://www.goodmorningkitty.com</link>
<description>A kitty a day keeps bad luck away</description>
<lastBuildDate>Mon, 12 May 2014 13:34:36 +0000</lastBuildDate>
<language>en-US</language>
<sy:updatePeriod>hourly</sy:updatePeriod>
<sy:updateFrequency>1</sy:updateFrequency>
<generator>https://www.ads-software.com/?v=3.9.1</generator>
</channel>
</rss>

Anyone knows what is happening?
Thanks in advance!