Hi,
Sometimes there can be problems saving raster images if you are not using Java. So if you are on a Windows pc, use Java.
I just tested saving a raster image I painted with a brush and it is working. I did not use Java and I used the Chrome web browser.
When Fatpaint uses Java, it will use it for saving raster images. If Java fails, it will fallback to using Flash, so this way, 2 mechanisms have to fail before you loose your work, making the app more robust.
You can also try using different web browsers, some work better with Fatpaint than others. I recommend the Chrome browser from Google.