Can't use Nero DVD-Speed with NEC2500A! Help!

I’ve burnt a few DVD movies using DVD Shrink + decrypter. These DVDs can be checked with Nero DVD-Speed using the read test.

However, more recently I have burnt a DVD with folders and files in it (backup of personal files). The files and folders were burnt by just drag and paste unlike the way I burnt the DVD movies. For some reason, Nero DVD-Speed won’t do the read test! Anyone know why? Should I be worried?

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