The DVD drive will not play DVD-Video discs of the region you just switched to. Instead, you see an alert box with this error message: "This DVD-Video disc has a region code that does not match the region code set for your DVD drive. You cannot change the region code for your DVD drive."
Symptom
The DVD drive will not play DVD-Video discs of the region you just switched to. Instead, you see an alert box with this error message:
Solution
2. Insert a single-region DVD-Video disc. Make sure the disc's region is the one you want to use to permanently set the DVD drive's region. For example, if you want the drive to play Region 2 discs, you should insert a disc that is only Region 2. Important: You will no longer be able to switch regions.
DVD-Video playback is normally restricted to one of six geographic regions. DVD-Video discs can usually only be played with a DVD player whose region matches the disc's. Apple's DVD solutions allow you to set or change your DVD drive's region setting up to five times. The last setting is permanently locked into the drive. When changing the region setting for the last time, you must use a DVD-Video disc approved for play in one region only.
For more information about DVD region encoding, see article 60183: "Apple DVD Player: DVD-Video Region Discussion"