When installing and running Office Excel 2013 on a host operating system where an Internet Explorer version earlier than IE9 apps will not work. Instead the the following error message will be displayed:
Sorry, we couldn’t load the app because your browser version is not supported. Click here for a list of supported browser versions.
Please note that the ISO-8601 week numbers are just one way of expressing week numbers and might not be what you want. The week numbers start on Mondays per definition and does not change when changing the week start day. If you would like to use another week numbering format you can still add a column using the =WEEKNUM(date, week number system) formula in Excel.