Genre transfer from WMP to Sansa Clip Zip doesn't always work

when I sync files to my Sansa Clip Zip most of the genres get transferred fine but some of them do not show up at all.  The albums are there but the genres are not.  There are two genres named “unknown” and “unknownk” (the misspelling is on the Sansa).  Eash of them have albums in them but are not consistent with anything. - they have mixed genres.

I would like to be able to listen to the files by genre.  Please let me know how to fix this.

Jim