Any reason why you want to move the 30th frame to render?  Why not just move the dial all the way to the right and render the last frame?

All I ever do when working with dynamic cloth is save the file as normal with all it's frames.  Then when I want to render a single image, I go to the frame I want to render and render that one frame, which is usually the very last one.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi