Can't View Second Session

Hi, I have come across a problem where I have backed up some .avi files to DVDR in more then one session and although I can see the files on the DVD on my computer my DVD player only sees the first session, if I burnt all the files in one session then it’s not a problem but I now have several DVD’s that are burnt in more then one session, is it possible to burn the DVD again to incorporate both sessions?
Zetor

Win XP Pro SP2
LG Writer GSA-4160B
Nero 6.6.1.4
LG DVD Player DVX9900H
Sony DVD+R