It is possible your CD RW is wore out. If it's not all the time, this would be my suggestion.
Has anyone had the problem of re-burning a RW CD in Picasa and then being unable to actually write to the disc after it has erased the original information. If so, how did you solve it. I've restarted my computer, restarted Picasa, double checked that my files are all the correct length, etc., but I'm still having this problem, just not every single time. Help!