what does this 'cdrom: open failed' message mean

[Alexander Volovics]

System Log/Kernel Startup Log contain the message:

May 10 12:05:15 if kernel: device-mapper: 4.1.0-ioctl (2003-12-10) initialised: dm at uk.sistina.com
May 10 12:05:15 if kernel: hdb: packet command error: status=0x51 { DriveReady SeekComplete Error }
May 10 12:05:15 if kernel: hdb: packet command error: error=0x51
May 10 12:05:15 if kernel: cdrom: open failed.

However the device seems to be working OK.
What triggers this message and can I just ignore it.

Alexander