Multisession Mounter is a Control Panel for mounting multi-partition
CDs on systems that are unable to load more than the first partition.
System 7.5.x or later should not require it, but if you are running a
system older than 7.5.x, or if you are running a Macintosh clone (such
as Umax), just copy Multisession Mounter to the System Folder and
reboot, after which the system should be able to mount multi-partition
(that is, "multisession") CDs without issue.