Hi there, & welcome to Tom's Hardware!
Not an uncommon occurrance, but difficult to pin down. First specifically identify if there is a relation to the OS on the computers that sees it OK, and the PC's that don't. For example Win-XP reads it, but Win-7 or Vista doesn't.
Also, if both the laptop and desktops can read the SATA connected directly, then it may be surge related bad component in the iomega case itself.