A little more info would be helpfull (format and speed). Media quality is the first thing to look at. If they are crappy disks, its possible that the ones that did work, marginally worked and the ones that are not working are a little bit lower quality. Another posibility is that you got two diffrent brands of media in the same pack. while most manufactures don't do this, some do (like memorex). Infiniti doesn't make any of thier own disks and it looks like out of the 7 diffrent formats and speeds they sell, thier are 22 diffrent brands they use. Some of them are crappy and some are good (not the strangest, many companies just use whatever they can get cheapest so sometimes it's good, sometimes it's crap).
If you have a dvd burner or dvd rom on your computer, download this free program
and find out the manufacture and media id (who really made the disks).
If not, about all I can sugest to try trouble shooting it is try diffrent media to start with. Staples have maxell on sale. Try some maxell dvd+r 4x. The 4x will usally be ricohjpnr01 (thats the true manufacture). I'm not sure about the liteon standalone burners like you have, but liteon computer burners generally love this media and support it very well (it is very good quality media). I wouldn't even be suprized if it burns it at 8x (many computer burners support burning it at 8x).
If you can post more info about the media you have perhaps we can help more.