I was in Eretz Yisroel for 2 weeks for a wedding. I apologize and I hope to get back to the regular posting.
R' Elchonon (kovetz hearos 30:7) raises the question whether the concept of ein issur chal al issur, prevents the second issur from being chal at all so that there is no prohibition regarding the second issur, or is it just a din in punishment that one cannot be punished for the second issur.
He proves from Tosafos who explains that the issur zarus is chal simultaneously with the issur neveila (by a bird that melikah was done to), since the issur neveila cannot be chal on top of the issur meilah, and the issur meila is only removed with the sprinkling of the blood, so both the issur zarus and the issur neveila are chal together at the time of sprinkling the blood. R' Elchonon points out, if the issur of neveila is actually chal at the time of melika but only in respect to punishment do we say that you can't be chayev for neveila until after zerika (so in respect to punishment alone neveila is chal at zerika), how can the issur zarus which only begins at zerika be chal on top of the issur neveila which is chal at the time of melika. From the fact that tosafos assumes that both zarus and neveila occur simultaneously at the time of zerika, it is clear that 'ein issur chal al issur' prevents even the issur neveila from being chal on top of the issur meilah.
R' Elchonon proves the same point from the Nekudah Nifla'ah of the Rambam in Krisus.