When a quiz is inserted into an Articulate Presenter presentation as a player tab, you may find that the lightbox that opens the quiz doesn't have a close (X) button in the upper right corner. There are a couple possible reasons for this behavior.
User can only leave the quiz after they've completed it
The quiz property Allow user to leave quiz must be set to At any time for the close button to appear throughout the quiz. If it's set to After user has completed quiz (which is the default option), the close button will only appear on the result slide at the end of the quiz.
The first slide in the quiz is a blank slide
If the first slide in the quiz is a blank slide (i.e., non-question slide), the close button may be missing—even if the Allow user to leave quiz property is correct (see above).
This issue was corrected in Update 2 for Articulate Studio '13. To take advantage of the new features and fixes, download and install the latest version from the link in your product confirmation email, or get it here. Then republish your project.