>If the files don't have a .TIF filename extension then add an extension to one of the files and then see if it will import.
Bob is right. That is probably the issue. Lightroom doesn't recognize the old filetype/creator metadata codes that Macs used to use 20 years ago so won't recognize that they are image files if there is no extension. You might not realize there is no extension as Mac OS X stupidly hides those by default. You should always turn that option off in the Finder presences->advanced.