At this point you can use the answerDiscussion.pl macro. However, the macro is out of date which results in the errors that you are seeing. Furthermore, in the future it will stop working entirely. For webwork2 it should continue to work (barring errors in the code). However, for webwork3 or anything that uses the standalone renderer it will cease to function.
If you can get the macro working again, a pull request to PG with the fixes would be appreciated.