transparency has been an issue in the past, but I can't find any crash links for pdf format for version 10.4.x within the last year. If this type of layout hasn't worked (ie with all the transparency and stuff) and other exports of simple maps work... then it is the map. If you can't export period, then that is a totally different issue. So try to export a very simple map, a simple map with transparency, your desired map without transparency and with. Failing that, open a support request with tech support.