ya + can be less compatible on some xbox's, let us know the results of the dvd-r
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Also, can you tell me what brand your xbox DVD drive is? If you dont know offhand use this image as a guide.
(This image is from the Noob Guide to Everything, if someone has a problem with me posting this image let me know and ill modify my post to link to the guide instead. Sorry if this inconveniences anyone...I'm just trying to be helpful)
Also what is the brand of DVD-R/+R that you are using? I cannot really confirm this, but I hear, the cheaper the media the less likely it is to work, so you get what you pay for. Most of the media I have purchased has been the dirt cheap stuff (maybe the reason i went through 3 packeages?) Just play around with different brands, and check the backup/burning forum because they also have a topic somewhere which deals with media compatibility. Good luck and let us know.