That happened to me several times. Once I edit an attached excel file in EN and save it then reopen it, I found all cells without formulas has their format changed to "Date" format ! that is really ruining my work ! I even have premium account ! Anyone experiencing this ? how to stop that ? I attached simple table in the excel file . see how all numbers changed to date. the lower cells are 1, 2, 3 but changed to 1-Jan-00, 2-Jan-00, 3-Jan-00 !