PS2 Slim Backups Won't Work W/ Swap Magic Coder Plus?

Ok so i have a ps2 slim model SCPH-79001. I have already modded it and i purchased swap magic. I insert swap magic and it works perfectly, now when i go to replace it with my iso. backup when needed, it goes to the red screen saying it can't read it. I burned my backup at 4X speed with a DVD+R. Please i need help with this.