D3-2 is the name of a new kind of drive for the Nintendo Wii.
Many newer Wii's and ALL black wii's have this drive.
People with this drive will never be able to play burned backup discs with that drive. If you still need to play your backups, but have one of these drives, you must use an USB loader (since they are not affected by the drive) or replace your drive by another one. You can also use Hermes' uLoader and load discs from an external DVD drive.
There is no real way to tell if your wii has this drive before you get it (unless you have a black wii).
If you have the serial number, you can calculate the chance of having a D3-2 drive with http://www.wiidrives.com/list
Affected by this issue:
All disc backup launchers (including gamecube backup launchers)
All Disc based ModChips (ModChips can still load from SD/USB if this is supported by the ModChip)
Any app that loads from DVD (Mplayer_CE, Emulators, ...)