Nah, my working theory is that save compatibility recalculation broke your quest somehow, another theory has to do with uninitialized variables in the dll.
This general problem with all quests appeared after v39 release, and the xml hasn't changed for any quests since then.
PPIO didn't modify any quest related python, so I'm pretty sure some of the very technical changes that hapopened in the dll after v39 release borked something with the cached data for running quests.
Edit: Wait.... are you playing on v39 when getting this error? Just realized what thread this is.
If someone could confirm this error happening on a game started on a more recent SVN then this problem would become high priority. If it is simply a one off case of broken save then its not that high priority to fix.
I'm pretty sure you can play on with your save without any serious consequences from those python exceptions. If this same exception is thrown often then you may want to hide python exception. This can be done in the BtS.ini file.
I should add this issue to our github bug tracker so the dll modders may take interest in it.