JSON error

using the plugin we’re getting the following error:

Something unexpected has happened along the way. The specific details are below:

textStatus: parsererror
errorThrown: SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

xhr.responseText:
<div id=”content-protector-unknown-error” class=”content-protector-incorrect-password”>Something unusual has happened. Content Protector cannot find your shortcode in this Post.</div>

Here is the shortcode:
[content_protector password=”password” cookie_expires=”15 minutes” identifier=”seville” ajax=”true”]

Any thoughts on how to resolve this?