Can't load MP3 files onto Sansa m200 get error 0 x 80070052

Want to load MP3 bird call files. Only 57.5 mb used and they were MP3 files loaded from same source without any problems. Now when I try to load the new batch which is 128mb containing 458 MP3 files error 0 x 80070052 .Would like this solved, please? I get I am a newbie to this technology.

Many thanks

Rod W