xbmc doesn't regognize dvd's in lubuntu 11.10

I have a medion PC MT6 with a cd-rw reader/writer an a dvd reader, I run XBMC in Lubuntu 11.10

When I put in a dvd in the dvd reader "PLay Disc" does not appear in the menu, but:

• when I put in a cd without media, e.g. a Windows software cd in the CD READER then "play disc" does appear in the menu but of course xbmc can't play the cd
• If I put an audio-cd in the CD READER "play disc" does appear in the menu and xbmc is able to play the cd.
• If I put an audio-cd in the CD-READER and a dvd in the DVD-reader then "play disc" appears in the menu and xbmc plays the audio-cd.
• If I put a Windows software cd in the CD-READER and a dvd in the DVD-reader then "play disc" appears in the menu and xbmc PLAYS THE DVD.
  

this means that xbmc only plays my dvd's when there is a non-media cd in the cd-reader.

Is there somebody who can help me to solve this problem or is there anyone who has the same problem?

regards

Niels