Facebook – IFTTT if Feed item then Facebook Photo never run

I want to forward the RSS feed of a vBulletin Forum to Facebook. If the posting contains an image, it should be displayed within the facebook post.

So I used the Recipe:

  if [New feed item from http://example.com/feed]
then [Upload a photo from URL on myFacebookPage]

This recipe is active since a week. Although there have been new items, they didn't get forwarded to facebook. Next to the recipe there is the text:

created May 05, 2015 never run

If I configure the recipe to upload them without a photo, everything works. Why does this not work for photos?

Here is an example what my feed looks like:

<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/" version="2.0">
    <channel>
        <title>bla</title>
        <link>https://example.com/</link>
        <description>Yep</description>
        <language>de</language>
        <lastBuildDate>Wed, 13 May 2015 11:00:38 GMT</lastBuildDate>
        <generator>vBulletin</generator>
        <ttl>15</ttl>
        <image>
            <url>https://example.com/misc/rss.png</url>
            <title>Here</title>
            <link>https://example.com/</link>
        </image>
        <item>
            <title><![CDATA[Bla]]></title>
            <link>https://example.com/threads/uniqueURL</link>
            <pubDate>Mon, 11 May 2015 18:32:11 GMT</pubDate>
            <description><![CDATA[ Some text and a graphic: https://example.com/someimage.png]]></description>
            <category domain="https://example.com/cat1">cat1</category>
            <dc:creator>Someone</dc:creator>
            <guid isPermaLink="true">https://example.com/threads/uniqueURL</guid>
        </item>
        <!-- More items -->
    </channel>
</rss>