Just for anyones info reading this thread... I was using a copied DVD Map on very cheap media and got "CD/DVD Error" on very hot days while driving around the south of France in my dark blue E46 with MKIV Sat Nav... Basically it stopped working..

It turns out that was down to the no-name brand cheap media not liking the heat.. > 30 deg C outside.. and pretty warm in the boot/trunk! I used another brand and have had no further problems...

Obviously your unit though and not the DVD in this case....