Copying files from Mac OS-X to the iRex iLiad reader creates .DS_Store files and ._ files on the iLiad. Sometimes this seems to be a problem – some PDFs could not be opened any more. Unfortunately those files are not visible in the OS-X finder. Connecting the iLiad to an WinXP computer allows to remove them but it is really clumsy having to use multiple computers.
Matt Jadud, wrote an OS-X a application called iliad-scrub which runs through the iLiad folder and cleans the files automatically. Thanks Matt!