Well, it says "SRAM" on the card itself and Prepcard actually detects it so I assume it should work. I also think I read a post somewhere at Amigaworld.net that the centennial SRAM card should work with the Amiga.
I suppose the only conclusion is that the card really is broken :-( . Btw, does it need drivers when used on a PC laptop? I have an old one on which I could try it before I scrap it.