I use excel for mac 2011 and record my time on one excel spreadsheet . Auto recover is enabled, I also have the spreadsheet in Dropbox with full recovery options. I also use time machine. One or possibly more tabs on an excel spreadsheet keep deleting the content, which cannot be recovered from any backup. Last week the problem arose for the second time. I kept hitting save, closed and opened the sheet and the work was obviously saved because it was there. This morning one tab , possibly two have lost the saved information again. The rest of the tabs seem fine and have not been deleted and have retained the new information I saved last week. I definatley saved the information on the tab that has once again deleted the new work. I need to recover it.