I investigated a little bit more and found out that if I burn a audio cd with the option enabled "burn the image directly without saving it to disc" which was default in brasero after upgrading to karmic the cd can't be read. But disabling this option produces now again valid data cds.
I investigated a little bit more and found out that if I burn a audio cd with the option enabled "burn the image directly without saving it to disc" which was default in brasero after upgrading to karmic the cd can't be read. But disabling this option produces now again valid data cds.