I don't have suggestions about particular brands of optical media.
But, the suggestion to try a different brand is a good one.
If you have not used Sony before, what other brands of rewriteables do you usually use?
I think Sony is a good brand (at least, I have not had more problems with Sony than other brands I have used)
If you have more Sony disks, have you tried another Sony disk?
Have you tried cleaning the drive? Even blowing into the slot with a 'can-o-air' might be helpful.
Have you burned lots of other disks in your burner? I have an old G5 tower that has been used for several thousand burns (and I've replaced the drive 2 or 3 times - I don't recall for sure). All the burners eventually go south after heavy use.
Personally, I don't like to use rewriteables, as I have not had good luck with reusing them. That makes it pointless for me to use rewriteables at all.
So - the question is: Do you really need to use rewriteables? (Have you used them successfully in the past?)
OR, is this a new task that you are just testing?
If another brand also does not burn properly - what is the error that you get (exact text)?