LOOKING FOR ANSWERS

LOOKING FOR ANSWERS
     
 שוגג  you are חייב בקרבן is when you erred in Halacha
eg: not being aware that you are not allowed to carry in a
רשות הרבים on Shabbos

מתעסק you are not חייב בקרבן is when you are not being
aware of the fact, eg: You carry on Shabbos believing
there are מחיצות but turns out to be no מחיצות.

Question:
If someone from out of town (not knowing anything) asks
the Rav if he may carry in the city on Shabbos. The Rav
assumed that all the מחיצות were up and told him that
he may carry. The Rav later discovered that one of the
מחיצות was down.

Is the person who carried relying on the Rav's Psak,
a מתעסק since the Rav's Psak was based on not being
aware of the fact,
Or do we say since he asked a Rav and the Rav
(mistakenly) answered, therefore, it is considered a 
mistake in Halacha and he is a שוגג.

I would very much appreciate an answer from the עולם