Can't access my cdrom

Having installed my Suse 7.3 on my atapi cdrom I have had no problems to access programs on the cd's via Yast2. Since short I cannot access them any more and asked for details after Yast2 keeps asking for a certain cd I get following information: Could not mount the source medium, mount: blockdevice /dev/sr0 is write protected, mounting read only mount: you must specify the file system type. I have not changed anything on my system, at least not knowingly and have no idea where to start looking for the error.