Obviously you have loaded something on them that they don’t agree with. Corrupted files or files with bad or the wrong format ID3 tags will cause this. Could only be one file; when building the dtabase during refresh, it encounters the problem and just stops, not knowing what to do with it.
ChkDsk will check for and fix corruption. MP3TAG will help you in editing and/or changing the tag format to ID3v2.3 8859-1 (Sansa’s favorite flavor of tag).
