My sansa Clip puts files in ''unknown'' Directory and doesn't play them when asked.

I need help!! I recently bought a 32gb micro sd card for my sansa, and the first time around, I filled the whole thing in one go. to my surprise and dissapointment, the ‘‘refreshing your files’’ message was very quick, and I noticed that only 1/100 of the files were actually there.  Some were also in the ‘‘unknown’’ directory, even though properly tagged. when I tried to play them It skipped right through them, like they were corrupted or something.

Now, I formatted both the sansa and sd card, and started putting files in slowly, refreshing it and checking the files I put on there every 3 folders. Everything was going smooth until I started getting the same thing, bits of folders being put in the ‘‘unknown’’ directory and skipping. What I did was plug it into my computer, delete the folder that goes in ‘‘unknown’’ and replace it with another. then the newer folder with files worked, but some of my previous files I put on the sd card go into the ‘‘unknown’’ even though they worked fine before. I’ve tried doing it for ages and it just goes in a loop like that.

I know my files are properly tagged, and CHKDSK doesn’t show up with any errors. 

As of now I have 670 songs and barely 3gb of the sd card is filled. I need solutions please.