My internal DVD writer broke down on my Mac, so I replaced it with an external USB LiteOn 8x External CD/DVD writer. Everything works fine, Music CD plays well, burns with Toast are alright. However, DVD player in OS X 10.5.8 was having problem when trying to play a DVD. The error message is "a valid drive could not be found error-70012." What the heck!
After some searching online, I found the solution. A big thank you. To patch the DVD player software so that it agrees to launch without an internal reader, go to System » Library » Frameworks » DVDPlayback.framework » Versions » A. Make a backup and a copy (i.e two different copies) of DVDPlayback on your Desktop.
Open the copy with a Hexadécimal editor such as HexEdit 220. Find the word (ASCII) Internal and replace with External or (hex) 496E7465726E616C and replacing with 45787465726E616C. There will be about 4 to 6 matches that need replacing. Save the file and replace the original with the edited version. So it is important to make and keep a backup copy of the original, in case you need to revert the changes. Because after the changes, any internal reader will not be supported any more.
For my case, I go Find & Replace in HexEdit (see below). Then Replace All.
Voilà! Now DVD player works with the external writer.
Applause for me. I am no pro, yet managed to settle it at once. Ho Ho !