When trying to play any video in MythVideo that is an ISO, it fails to play. Playing other types of videos is fine.
Storage Groups are a streaming method of transmitting material to a frontend, meaning they don't provide block-level access to the file in question. An ISO is a disk image, and libdvdnav/libdvdcss, the libraries used to view DVDs/DVD images, requires block-level access. See MythVideo - Disadvantages
This is resolved in MythTV 0.24 and later