Wordpress: 3.5.1
Wordpress SEO: 1.4.4 (And Developer)
I added the Twitter Cards Markup using your Wordpress SEO plugin, and entered my twitter account: vithefiddler.
This is the code that is generated when this is enabled. It doesn't validate with the Twitter Cards Preview tool because the creator is invalid. It should just be @vithefiddler, not @http://twitter.com/vithefiddler/
I did disable all of the other plugins I have installed, and also looked for the URL in the wp_options table of the database just to be certain that it was coming from the plugin.
<meta name="twitter:card" content="summary"/>
<meta name="twitter:site" content="@vithefiddler"/>
<meta name="twitter:creator" content="@http://twitter.com/vithefiddler"/>
<meta name='twitter:image' content='http://www.vithefiddler.com/wp-content/uploads/2013/03/suzuki-violin-and-fiddle-workshop-300x262.png'/>
<meta name="twitter:description" content="I’m really excited to be teaching the fiddling portion of the Violin Celebration: Suzuki and the Fiddler this June. I’m so excited for this event that I’m actually going to leave Weiser early to teach at it. I know – it’s hard to believe. Here is the official information direct from the flyer: A Violinist’s [...]"/>
<meta name="twitter:title" content="Suzuki Violin and Fiddle Workshop - Vi Wickam"/>
<meta name="twitter:url" content="http://www.vithefiddler.com/suzuki-violin-and-fiddle-workshop/"/>Thanks for your help!
Vi