Tags are electronic labels in the files. The Clip reads the tags and makes lists (not folders) of Artist, Album, Title, Genre, etc.
But if it can’t read the tags or the tags aren’t there it considers them Unknown.
The Sansa likes tags in the format ID3v2.3 and will also read ID3v2.2. It won’t read ID3v1 at all, and ID3v2.4 can also give it trouble.
My guess is that the tags are in a format the Clip can’t read. This is super easy to fix.
Get the free program mp3tag. http://www.mp3tag.de/en/
When you install it let it add itself to context menus (an option while installing).
After it installs, open it and go to Tools/Options/Tags/Mpeg and under Write oID3v2.3 and ISO-8859-1. (ISO-8859-1 is how Windows displays English language text.) Make sure those are saved.
Take your problem album off the Clip (and if you don’t already have it on your computer, copy it to your computer). Right-click the album on your computer, choose Mp3tag from the menu to open it and you’ll see all the songs.
Look at the ID3 version. Bet it’s ID3v1 or ID3v2.4–trouble.
Make sure they are in playing order from top to bottom (you can click on the Track Number column header if you need to). Highlight them all and go to Tools/Auto-Numbering Wizard and choose Leading Zeroes. This will number the tracks 01, 02, etc. (Otherwise the clip will play 1, 11, 12, 13, 2, 21, 22, 23, 3 etc.) And it will also save them as ID3v2.3 ISO-8859-1.
Or, if artist names are the problem, look at the Artist column and see if the info is correct. You can highlight all the files, put the Artist name in the box on the left, and Save them all at once. This is good for consistent naming.
It’s complicated to explain but it takes seconds to actually do. I do the Auto-Numbering thing with every album I get before it goes on the player. It’s 2 or 3 clicks and done.
If you keep clicking down past Artist, Album etc., onto a second page, you’ll see Folders. Those are actual folders and your album should be there.