Well, it seems to me that the Church’s teaching on this issue is different before and after Vatican II. Before it was declared sinful, but after Vatican II it was said to be good to attend them.
If you are asking if it’s ok to attend protestant services…the answer is yes in most cases as long as your sunday obligation is fulfilled. If you’re asking about attending services at the “catholic” church down the street that has the female priest…the answer is no.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.