I think your latest problem is when you save a render, you first have to save in a format and location, then when you render it will save to that location. Generally you do than in the render tab. I would have to check in v9.0 it has a render globals tab that might do the same.
If you don't you will get that error message (not that I ever do -- lol )

alot of times when I am experimenting; I will render a quick preview and then save the image from the render window itself.
and you will always get the "abort render yes or know" question when you render.