first I'm new to this so sorry if I double post on something that is already done.

I am trying to decompile Shared.artwork but keep getting

C:\Users\User\iPod\artwork>java -jar iPhoneShop-1.3.jar artwork Shared.artwork export pngs
Exception in thread "main" java.lang.IllegalArgumentException: Unsupported artwork type
at ee.rumba.iPhoneShop.artwork.Artwork.<init>(Artwork .java:202)
at ee.rumba.iPhoneShop.artwork.Main.main( )
at ee.rumba.iPhoneShop.iPhoneShop.main(Unknown Source)

does anyone have any ideas on how to fix this?