===Icon file has to be put inside the same directory as manifest.sii file.===
The mod icon file should be placed next to the manifest.sii file in the version folder/archive. You need to move it or create in case you have not done it yet.
===Icon file must be JPG file (?)===
===Incorrect icon file dimmensions. Allowed dimmensions are ?x?px (the icon size: ?x?px)===