Some of the songs I put on my memory card won't work...why?

I have an LG Banter and just got a memory card for it. I loaded like 10 songs from my itunes on it (copied and pasted them to the memory card) and only 3 of the songs show up on my phone. I put them all on the same way from the same computer from the same itunes...but they don't all work. Does anyone know why and what I can do to make them all work??