Thanks for the picture.
Strange thing indeed - does anybody have a clue of why this could be happening?
Essentially, "mount -o ro /dev/sr1 /media/cdrom" fails for some obscure reason. However,
- The mountpoint /media/cdrom definitely exists, so that's not the reason.
- The device name is taken from /proc/sys/dev/cdrom/info, so the system at least *knows* that there is a CD drive. And hopefully, it also lists the correct device name
- Last not least - the CD drive obviously works, otherwise it wouldn't have booted in the first place.