Well, I don’t recall having this problem before, but when I minimize a rendered picture, I cannot zoom in with the middle mouse button. I know this seems like a small, insiginificant, if inconvenient, thing, but it would help loads to be able to do this to work on my dragon. Any thoughts? Am I just being whiney? Well, so it doesn’t sound like I’m just complaining, props go out to all the coders out there; thanks a Ton. 
you probably have to bring focus to the blender window
instead of minimizing the render window, press F11 to switch to the blender window, then it should work fine.