I have a sheet that I shared with my coworkers where every other column has a drop down menu and it's corresponding column next to it has a formula to timestamp the week the cell was last edited. Yesterday every single cell containing that formula gave an #N/A error. I believe it is because an individual opened it in a different version of excel that couldn't use the functions in the formula properly.Is there any way to change this formula so I still functions the way I need it to without the risk of if erroring out. =IF(E17<>"",IF(AND(F17<>"",CELL("address")=ADDRESS(ROW(E17),COLUMN(E17))),ISOWEEKNUM(TODAY()),IF(CELL("address")<>ADDRESS(ROW(E17),COLUMN(E17)),F17,ISOWEEKNUM(TODAY()))),"")
I guess it's ISOWEEKNUM that creates the problem. This function has been introduced with Excel 2013, so if someone with Excel 2010 / 2007 opens it, you are in trouble. All other functions should be uncritical.