If you're not rendering with Corona, then rendering should work as normal (if it always has before). Total memory used depends on what other applications are running at the time, so could be more running this time (or some update has made one more memory hungry). Could be something about this scene just happens to need more memory (more geometry, larger textures, more textures, more instances or cloners, more displacement, etc.).
Even if this message popped up with Corona, it normally just means things will render but will render more slowly (same could be true on the other engine, just it doesn't have a warning dialog to tell you that ;) )