2010 hatchback, ERROR 18 (CD player won't play)

Hi everyone, bought my first car recently its a 2010 aveo hatchback. When i bought it everything electrical was in working order apart from setting 3 on the fan this however was promptly fixed under the warrenty. The other day however i decided to put a cd into the factory fitted radio (which works perfectly fine on the radio setting) as the cd enter the screen portrayed "ERROR 18" and spat the cd back out. Now the player wont accept any cd's and when eject is pressed it hums as if it is releasing a cd. Does anyone has any idea why this may of happened, info is greatly appreciated.
Cheers