The pic has to be sized correctly-this is what I do and it's kind of obnoxious so maybe someone has a better way; but I use my computer's "Paint" program to reduce the image size until the pixels are within the boundaries, and then upload it.
If you have photoshop you can do it that way too. What is the image size on here? Most forums have 100x100 but I noticed it's "longer" for here. 100x100 is a safe size to make icons at if you do it as a hobby.