Trak error or Disc error

I bought a DP Video car stereo in november last year when I was in Dallas forthworh for school traning. I have installed the unit to my car successfully. The stereo does what it is supposed to do but when I insert a DVD to play a movie, the sound is there but the screen shows "Warning - DO Not watch movie while driving". I solve this problem by connecting the ground wire to antena.The unit did not come with a manual.Now another problem appear is when I insert audio cd there is a mesage on display says disc error or track error.HELP

Regards,
wilson Matuno