Not all the source code of ISAAC is available.
Concerning the (I have to admit ‘cryptic’) error you get, it comes from the fact that the Pose the GlobalPlanner is getting is in a coordinate frame not connected to the world. (From your other post I understand you did not understand what the planFrame was for, and if you provided a frame not existing in the PoseTree you will have gotten this error).
Thank you for reporting, I will make sure to update this error message to be more useful.
And to fix your own issue, you should specify the planFrame to the frame of your poses (most likely “world” if it’s absolute, or “robot” if it is relative to the current position).
I hope it helps!