Bad batch of cards, or reader/writer issue?

[rprosperi]

I can also support the eraser cleaning method. It seems to remove thin, seemingly invisible layers of oxide that prevents clear reading (by 'invisible' I mean the eraser crumbs that come off do not appear to be excessively dirty). It works quite well, but it is VERY EASY to destroy a card, by the eraser 'catching' the card with friction and suddenly bending the card, ruining it. I recommend you practice the technique on an already known-bad card, or a new one that you can spare, in order to get a feel for what it's like. Work on only small portions (0.5" / 12-14mm) at a time.