Hmm, Im not sure regardless of what format you put it in the end it's converted to .icn format. Unity does this automatically? I don't see how my problems with just changing icon needing a reinstall, but don't mean to doubt you
Edit: I think it can't use those formats when the makebanner is doing it's thing to make the icon I tried all types even. tga (Can you share your icon?)
Edit: I guess I'm reinstalling guess I tried a bunch of formats