OSMC

I am trying to install Kodie via instructions in Raspberry Pi Tricks mag. It says to install OSMC on an SD card that has the os on it. So I installed Noobs and loaded Rhaspian. Then inserted the same SD card to install OSMC but am getting an error. I previously installed on a clean sd card and it all worked. I thought I had made an error though as I never put the OS on first. I hope this makes sense. It's all very new to me but I am trying.