The most likely problem is the device is running out of memory. We're working with the Scirra guys to find a way to load/unload images as they are needed, but for the moment CocoonJS loads all images on startup, and it needs enough memory to do that.
Also, image compression doesn't help at all for this, as images are decompressed when loading them into the graphics card. So, for the purpose of in-game memory usage, it's like if you were using BMP images (or uncompressed TIFF images for the ones with alpha channel).
There's also the issue of NPOT textures, which makes textures of 513x513 pixels use memory as a 1024x1024 texture, for example. Always try to reduce images to power-of-two sizes (or tightly pack several small images into a bigger POT one) if you are able to do so. Otherwise you'll be wasting lots of GPU memory.
Until we implement a way to load/unload images on request, our suggestion is to reduce the images size until they fit in memory.