When I try converting XLS to XLSX files, they appear to save correctly. But when I open and modify them, they open in compatibility mode with file names like "X000013" instead of the original file name, and are read-only. Also, converted files don't show up on the jump list. I even tried copying the text of one such file to a Word document , clearing the copy, and copying from that to a fresh XLSX file. The problem persists.