Error 49 - Encoding error

I'm trying to encode a magnetic card with a "Zebra ZXP Series 3", so I've download the SDK. I try to do it with the .NET utility, that it comes with the SDK, but allways get the same error "Error 49 Encoding Error". When I read the card with a card read this is the only data: "ñ12345678_"
Why it could be? I've already get the last SDK and the last drivers. By this time I'm lost because I don't have any idea of what could be happening