I just bought a MIDI to USB cable so I could connect my electronic piano/keyboard to my mac mini. I open GarageBand and the keyboard will play one note at a time just fine, but if I play two or more notes at once, then the sound will kind of spaz out, with the two or three notes just lasting forever and no sound from any new notes being played. The sound only stops if I hit the spacebar about two or three times (to press play and stop).

The keyboard and mac mini I'm using never did this with the last MIDI to USB cable I had been using previously, I only stopped using that one because it was borrowed and I had to return it. The new looks pretty much the same as the old one though, are MIDI to USB cables not all created equal or something? How can I get GarageBand to play/record what I play even when I press more than one note?