OS X 10.10 (Yosemite) & Cubase 7/7.5?

Did you use the Yosemite install tool, when you installed. It is apparently required at the moment:
http://www.steinberg.net/en/newsandevents/news/newsdetail/article/official-letter-on-yosemite-update-2837.html

Check out orchetect’s excellent posting here: