Sony AVD - S50ES Question

Hi Everyone,
This is my first post and need a bit of help. I'm in NTSC land (U.S.A) ,and a bit new to the digital age .
When playing back a DVD on the Sony AVD S50ES (AMP./REC./CD/DVD ) the image "stutters" to a slow motion effect for a few seconds at the start of the DVD , it then settles down and plays ok. Also on occasions it will not play at all and give the message "can't play". I eject the tray, start again and then it reads and plays. I have a region free Phillips DVD which plays just fine and doesn't do this. Does anyone have a suggestion as to what might be the cause of this.
Thank you.