If the built in drag and drop functionality doesn't work the way you want, then you might be able to try the Interactive Drag and Drop widget from Infosemantics.
Free trial version can be downloaded here: http://www.infosemantics.com.au/adobe-captivate-widgets/download-free- trial-widgets
I'm suggesting you try the Interactive Drag and Drop Widget rather than it's older sibling the Drag and Drop Lite Question Widget because the interactive widget can be reset on re-entering the slide, whereas the question widget behaves like all other quiz question slides and will not reset unless you go past the Retake Quiz button on the Quiz Results slide.
With the Interactive widget as well, you have Success and Failure captions that automatically display. You can even set preferences in the Widget Properties dialog to have the widget Reset its Success/failure Criteria after each Action. Another setting can Disable Continue so that the timeline does not advance while the learner is playing with the interaction.
Only caveat with these widgets is that they are NOT HTML5 compatible. If that's not essential to you, then they might be the solution.