Yes, it could be a card problem.
But it’s more likely that your new songs have tags–the electronic labels in the files for Album, Artist, etc.–that are giving the Sansa heartburn. Take your newly added songs off the Clip and fix them on the computer.
If you are on Windows get the free program mp3tag.
Download the file that’s named mp3tag(version)setup.exe, not the big green download buttons. When installing, allow it to add to context menus.
If you are on a Mac get Kid3.
I’m familiar with mp3tag because I’m on Windows. Kid3, you’ll have to be a little resourceful.
Tags aren’t standardized–they are in various version (ID3 versions, as in Kid3) and alphabets. In the tagging programs, change the default settings to write ID3v2.3 ISO-8859-1. Those are the tags the Sansa can digest. It’s in Tools/Options/Tags/Mpeg in mp3tag. And it’s somewhere in Options or Settings in Kid3. Make sure you save that as the default.
If you’re using mp3tag, go to the album folder, right-click and choose mp3tag to open it with. The songs should all appear. Highlight them all and Save them, which will make them ID3v2.3 ISO-8859-1.
Does cover art appear on the lower left when you highlight? Someone has imbedded the album cover in every song–no wonder the Sansa is choking. Go to View/Extended Tags. Click on the little floppy disc icon on the right to save just one copy of the album art in the folder. Then click on the X to remove the imbedded art from the tags. While you’re looking, see if there are long Comments, weird alphabets, etc… that might confuse the poor little Sansa’s tiny brain. You can <blank> out Comments.
Whenever I get a new album, I just run it through mp3tag before it goes on the Sansa. Another thing to clean up the album is to make sure the tracks are listed in playing order, top to bottom, and then Tools/Auto-numbering Wizard/Leading Zeros, which makes them 01, 02, 03, etc. You don’t even have to Save after that–they’re fixed, and the Sansa likes those leading zeroes. And if you see imbedded art, get it out of there before sending the music over.
You can also test the card for defects with the program h2testw, but that will erase everything on it so make sure you have copies.