I have not had any problems with Mp3's since I started burning at 8x on cheaper CDR's rather than 40x etc. It does to a degree depend on the CDR's used as some as you know are better quality than others, therefore are able to be burnt at a significantly faster speed.

Try burning at a slower speed in the first instance, perhaps even 4x if the CDR's are particularly poor quality.
I particularly like "Taiyo Yuden" media. They have always been very good for me and have a excellent reputation. They are also cheap enough not to worry about which is a bonus and burn successfully at 40x.