You said the Nero Speed test works right if you perform it with your burner. Are you doing the ‘Tranfer Rate’ test? Are you getting a clean line like this (it can be a bit more ragged):
Does the burn play right in your standalone? Have you tried other media?
If the Transfer Test looks good in the NEC and it plays right in your computer and standalone I would not concern myself with the reader’s test. With the almost infinite combination of hardware/software/drivers/firmware out there it stands to reason that somethings my not work for everyone.
You want a playable DVD, have you achieved that? That would be the only test I would really be concerned with.