ID3 tags: pieces of data put into music or spoken word files that identify the files by categories of information, typically artist/author, track name, genre, year, and album/audiobook/podcast series name. Sometimes files come this way, with the tags pre-filled in, from whomever created the files. Modern players use this information to create a database of the files on the player, that you can use to choose music or spoken word files from, under categories such as artist, song titles, genre, year, etc. If your files don’t already have the ID3 tags filled in, you can use Internet freeware such as MP3Tag, a tag editor, to add the information; Microsoft Windows also will edit the tags. http://www.mp3tag.de/en/
Like other players, the Clip+ uses ID3 tags to display what’s playing and to allow you to choose what to play. You also can choose what to play on the Clip+ without the use of ID3 tags, by using the Folders option at the bottom of the Clip+'s Music listing–navigation there is done by folder and file names, just like on your computer.
The Mac issue (note: I’m not a Mac guy–this is based on what I’ve learned here): when a Mac is used to copy and transfer music/spoken word files to a device, the Mac automatically, in addition to copying and transferring the files, creates and transfers small data files that Macs use for some purpose or other–“ghost” files. These extra data files cause the Clip to choke. Windows users don’t have this issue, as Windows-based computers do not create and transfer such data files.
My hunch is, the issues you are having are being caused by your Mac.
My recommendation would be, first, to clean up your player and erase the files on it–if you use the Format option under your player’s System settings, it will erase all the media content on your player. And then second, if you are using a Mac, use Kopymac to transfer files to your player (and it seems to be an easy program to use)–this may answer all your issues, easily. (Or, of course, you could use a Windows-based computer, or one using Linux, to transfer files to your player, to avoid the issue to begin with.)
You also can use something called dot_command, a command built into Macs, to clean up the extraneous file situation–here is a thread about that (and you can use the search box at the top right to find many others). http://forums.sandisk.com/t5/Clip-Clip/Mp3-files-are-creating-ghost-file/td-p/132721
I hope this information helps.