Looking at your current signature, it seems that you are using [sigpic][/sigpic]. I don't know why, but it won't accept the album link. Just download the image to your computer and upload it from there at using option 2 (Upload Image From Your Computer) and it should work. I tested it and it works for me.
Ps. As of now, signature limits are 600x160 and 100kb so size should not be a problem.
