Feed Error: The data could not be converted to UTF-8

i migrated Xibo 1.4.2 to version 1.7.9. When i try to run a ticker is no longer displayed the RSS feeds.
In the log, the following message is traced:

Feed Error: The data could not be converted to UTF-8. You MUST have either the iconv or mbstring extension installed. Upgrading to PHP 5.x (which includes iconv) is highly recommended.

The installed PHP version is 5.3.17
The enabled iconv library version is 2.11.3
The mbstring Multibyte Support is enabled

Can you help me please?

Did you make this upgrade in one step ie 1.4.2 -> 1.7.9?

Is the ticker on your old layout or new layout created in 1.7.9?
Can you share the rss feed url so we can test it?

Yes Peter,
the ticker is on new layout created in 1.7.9.

The rss feed url correspondes to a private php page that generates an xml using MySql data

This is the xml result

<?xml version="1.0" encoding="utf-8" ?>
<rss version="2.0">
<title>Feed RSS</title>
<description><![CDATA[Desctiption of address]]></description>
<pubDate>Mon, 23 Jan 2017 10:00:20 +0000</pubDate>
<description><![CDATA[Location, address]]></description>