I experienced this same bug, some cd's could be read fine but data dvd's refused to be mounted and I would receive the error mentioned above. Switching the iso and udf as mentioned above seemed to resolve this issue as I can now mount both automatically.
-- UDF disks don't get dynamically mounted https://launchpad.net/bugs/50640 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
