Downloading the latest image from (http://repo.onion.io/omega/images) did the trick. I'm now back to the Onion OS.
I'm still vague on why I might be running out of memory. I'm confused because the image size is always the same (16252928 bytes). Even for the different images on the repo site. It seems like this is normal, but I don't understand it. Perhaps the image size is always the same, regardless of what it contains. If that is true, do you (or does anyone) know how to determine what a given image contains?
Thanks again for your reply.