thank you WPyogi --
As soon as I realized the Pinterest button wasn't working, I contacted Shareholic tech support (before contacting anyone else). They were the ones who identified the metatag in my header.
<meta name="pinterest" content="nopin"/></head>
Here are the things I've already done:
1) Deactivated all plugins (with the exception of the Pinterest button plugin)
2) Reverted to the default WP Theme Twenty Eleven
3) Validated my site for Pinterest
4) Initiated tickets with my host, Pinterest, the theme developer company, and others.
Speaking of the no pin meta tag, StudioPress tech support said:
That is the rendered HTML source of the page after all the code runs. It does not say what plugin or action has added the code.
Unless someone manually added it to the theme files, I really have no idea where it is. We do not add that code to the theme files.
So I'm still stuck at square one. I want to permit pinning but somehow there is a line of code that is preventing that from happening and I have no idea how to remove it.