I found the problem. When upgrading to Dapper, a new user called
haldaemon was created. However it was not part of the cdrom group, and so couldn't access /dev/cdrom. I solved the problem by typing the command:
adduser haldaemon cdrom
Now it works fine. I still think it's an upgrade bug. The haldaemon user should have been added automatically.
I found the problem. When upgrading to Dapper, a new user called
haldaemon was created. However it was not part of the cdrom group, and so couldn't access /dev/cdrom. I solved the problem by typing the command:
adduser haldaemon cdrom
Now it works fine. I still think it's an upgrade bug. The haldaemon user should have been added automatically.