Mp4 WHAT IS THIS ..! HELP?

I PURCHASED THE hd, EXACTI VPC-GH1EX ..........AFTER I CHECKED OUT THE CAMCORDER..AND TRIED TO PLAY IT BACK THROUGH MY LAPTOP..THEN I GOT THE MESSAGE SAYING ....THE FILE THAT YOU ARE ATTEMPTING TOO PLAY HAS AN EXTENTION MP4...PLAYING THIS FILE MAY RESULT IN UNEXPECTED BEHAVIOUR ....AND IT DOES AS THE VIDEO PLAYBACK IS JERKY , AS IF IT IS PLAYING ONE FRAME AT A TIME TERRIBLE.!!....WHAT MUST I DO SO IT WILL RUN SMOOTHLY...DOES ANYONE KNOW HOW TO FIX THIS PLEASE, AND IF YOU HAVE THE ANSWER ....REMEMBER I AM ON THE SLOW SIDE AND 66...BAD COMBINATION ...CHEERS ..r