I think I have the same problem, although I never noticed it as a read problem. I have two Sony AW-G170A's (one with the original firmware 1.71, and one I've since flashed to Optiarc 1.04 firmware). Both worked fine when I originally purchased them and could burn and read both +'s and -'s (I burnt off the best part of a stack of 100 DVDs). And like a few other posters in this thread, I tend to hoard data over a months or years time then go on a massive DVD burning spree and burn everything off.

Anyways I didn't burn anything off for a few months then tried again, and had no luck what-so-ever. After posting here I figured it was just the rubbish media I was using, but as I posted in my thread, a brand new box of Verbatim 16x -R's wouldn't burn. So I tried a + disk and it was fine, then I saw this thread here.

Reading through all 10 pages, there's a bunch of solutions here, some of which I'll try after posting this, but still no definitive answer about how to fix/work-a-round this problem.