Nero problems! need immediate help

i burn a lot of movies on to cdr just to back them up (so in data format). Two days ago, i burned a 700mb cd fine and then i tried to play it back on my computer and it says that the file is corrupt. So I burned 2 100mb friends episodes on a cd and they worked fine. Why is it not burning larger files correctly? please help i have no space on my computer!!
Thanks in advance

does anyone have any ideas?

okay so I can burn a full cd of music with no problem. but I cant burn a full cd with one large file

It could be a number of things really, try to burn at a slower speed or if you can burn a 600-650meg file and see if that works.
On my computer it takes longer for a large MPEG to be read of a cd then off the hard disc purely because CD are read at a much slower speed, so it pops up, but it just takes longer.
You could also try verifying the disc after burning it (Nero has this option and I think most of them do now as well).