Sony DRU-830A, read problems with recorded DVD-R s

I am having problems with my Sony DRU-830A, and it’s only five days after the purchase.

The drive burns correctly CDs, DVD-Rs, DVR-RWs, reads them. But starting from today it refuses to read DVD-Rs, still continue to read all other formats and as well burning DVD-Rs.

In first days it read DVD-Rs

I have called the Sony’s UK hotline, they suggested upgrading my firmware and that’s what I did. I upgraded it from SS23 to SS25. Still the problem persists.

Anyone has experienced those problems? And there is any solution to this?

And I suspect that the drive burns DVDs little bit slowly.

Thanks in advance.