Reset answer on try again?

Glen,

Instead of using "hide layer" try using "Jump to slide, this slide, when user clicks Try Again."  Then set the revisit properties to "Reset to initial state."  That worked for me on the drag and drop questions.

Because you are starting from the initial state, it will not count your attempts correctly, so you will also need to add 2 triggers to the Try Again layer.  Create a TryAgain variable and say, When the timeline starts on the Try Again layer, add 1 to the TryAgain variable.  Another trigger on this layer will say, Show layer, Incorrect, it TryAgain is greater than 1 (or what ever you want to use for number of attempts).  

I hope this works for you.