I recently ran into a user who was getting the following error message every time they attempted to open their SharePoint 2013 site via the web interface in SharePoint Designer.
This action couldn’t be performed because Office doesn’t recognize the command it was given.
The pop-up message will look like the image below.
The user had both SharePoint Designer 2010 and SharePoint Designer 2013 installed on their PC, which should not be an issue specifially as you can have both on the same computer without issues. You may find when you upgrade a particular SharePoint 2010 farm that your users will need to clear their SharePoint Designer cache in order for the new 2013 designer to work. The cache was not the issue here though.
We found that the simple solution to the error was to re-install SharePoint Designer 2013 on the users workstation.
That simple action fixed the issue. The user had tried a repair of Designer which did no help, so a full uninstall then install was needed.
Hopefully this helps you if you run into this issue.