I'm thinking that it is a problem with this type of CD player.  I also have a Kawasaki 5dvd players and it does the same thing.
I has something to do with the way the DVD was recored.
Try pressing the NTSC/PAL button on the remote control.  The Unit and the disc region numbers are incompatible.
Sometimes this works,   sometimes it doesn't.
Good luck.
I have one particular DVD that will play in everyone elses DVD player, but my players gives me an invalid disc message.
                
 tvanderwor
                
 January 2006