Your markup is valid HTML5+Microdata and you are using the Schema.org vocabulary appropriately.
With “validator”, you probably refer to Google’s Structured Data Testing Tool. Note that errors shown in this tool don’t necessarily mean that your markup is wrong; they often mean that you won’t get a certain Google search result feature unless you provide certain properties.
If you want to get this search result feature in Google Search (e.g., the Article Rich Snippet), you have to provide an
ImageObject item as value (instead of a URL value) for the
<div itemscope itemprop="publisher" itemtype="http://schema.org/Organization"> <div itemprop="logo" itemscope itemtype="http://schema.org/ImageObject"> <img itemprop="url" src="https://www.mysite.de/resources/assets/71/small/my_logo_web.png" /> <!-- and Google probably requires some more properties here, e.g. "height" and "width" --> </div> <span itemprop="name">My Company</span> </div>