BleepingComputer.com: Burning Problem

Hi, im having a weird problem, you see..
first i burned some data files into a new dvd, closed sesssion, as i would do with any cd, the computer ejected the dvd, and so far no problem
then i reinsert it and do the same (burn new files), it starts burning and then... closes session and ejects the same dvd and...when i want to see it if burned correctly, i can only see the files i burned the first time. the point is that the free space of the dvd is considerely reduced, just as if it had burned the new files correctly, but there are no new files...
the weird thing is that when i inserted this dvd into a windows xp computer , the new files are there... why cant i see the files in the computer with windows vista i used to burn them? hope someone knows about this issue...