It's not being zipped, don't worry - .ace is an old form of archive of some sort, from my understanding, which is also coincidentally a type of file WinRAR defaults itself to be the program to open. So, it thinks "ooh, a .ace file, it must be an archive", when in fact it's your normal image (which is why it's saying it may be damaged - it can't read it because it's an image, not an archive). Just use it as normal and you should be fine.