Are you sure it's of the right dimensions? The dimensions are 85 by 85 pixels. The image has to fall within that size AND the file size, which I think is 488.3 kilobytes. If the size doesn't fall under both these size limits, it won't work.

Another thing, what file format are you using? I think the site only supports .jpeg and .gif formats. I believe .bit formats are too dense in data for the site to handle.

Edit: Looks like you figured it out now.