Esef Sf2 Player

Someone mentioned the esef VSTi, which is a soundfont player. I downloaded it and it works, except for the fact that if I don’t play slow, sometimes instead of one note being played, two notes are played: the one I’m playing in the keyboard at the moment and the previous one. It’s quite annoying: I can’t use it like this. Has anyone had the same problem? Doesn anyone know the solution?