RW media are tricky. First, they say they take speeds "up to", but in my experience slow and easy does it. Set up the write speed as slow as possible. You may need some burning software for that, as MS built-in can be spotty. I am unsure whether MS's built-in allows selection of write speed.
Secondly: unfortunately producing reliable RW requires good manufacture. I never had problems with Sony RWs, but Verbatim/Memorex/previously-unknown-MFR had their issues. This may be media issue, so I would RTS'd them. I personally stick to TDK's as they ALWAYS come through. Admittedly, I've dropped RW in favour of USB's/email/cloud, so now basically just Rs. But they are in data media like Canon is in printing (pop it in and it works).
Thirdly: whenever possible, I'm using +R/RW instead of -R/RW. I've found it much more stable and reliable, with much fewer issues during and after writing, and then later use.
Last thing: how old is the burner itself? Current crop of drives are pretty reliable up to one year with normal use, after that beam power drops significantly, causing issues exactly like this.
Update: I just remembered that RW does not like exposure to strong light, especially sunlight. It has to do with technology. I had several going bad after checking them for scratches against window in summer/ strong sunlight.
