The cause appears to be the use of non-ASCII characters in file names. Microsoft describes it like so: “Any user may be ...

OneDrive users may experience issues while opening a file in the ‘Available when online’ status. At such times, you may see an error message box – Can’t open ...

Microsoft has started looking into a problem that is preventing users from opening some Excel file attachments with non-ASCII ...

As spotted by Bleeping Computer, Microsoft has published a new service alert related to Outlook. Labelled as issue EX1189359 and titled "Users may be unable to open Excel files attached to email ...

You need to make sure that opening the app has administrator privileges. For that, you can right-click on the app and select Run as an administrator. If you want to always run the program as an ...

Oh, and yeah, you can't 'open' multiple types of files at once since they would not all 'open' in the same software. I suppose you could make a feature request to Microsoft to add that capability, it ...

Microsoft is working to resolve a known issue that prevents some users from opening Excel email attachments in the new Outlook client.