This problem has been around for a while apparently. Not sure if the authors have much interest in getting this fixed or not... which is too bad because it seems to do a good job, except for this bug. Apparently 2.5.1 works without the bug.... go figure.
You may want to seek an alternative to this plugin... I have a mission critcal prject where this error is unacceptable.
Error: 'null' is null or not an object