I work in Excel 2013, under Windows 8, and when I access the Review - Protect Workbook, in the "Protect Structure and Windows" window the "Windows" option is grayed out. My workbook is not shared or protected in any other way. I tried creating a new workbook to see what happens: even if I have absolutely no content in the workbook, the "Windows" option is still grayed out. Can anyone please give me an idea as to why the option is not available? Thank you.