Napa is a great way to get started building SharePoint 2013 apps with Office 365. It provides you an easy-to-use editor that allows you make changes to your app right in your browser. One nice feature it has is to allow you to take what you built and import it as a Visual Studio project. This is done using the Open in Visual Studio link at the bottom of the page.
If you are editing this in Internet Explorer on a server operating system such as Windows Server 2008 R2 or Windows Server 2012, you might encounter the following error.
xxxxx couldn’t be downloaded.
As you might guess this is caused by a browser setting. You can use another browser of course, but if that’s not an option, you can fix this by unchecking the Do not save unencrypted pages to disk checkbox.
Once you uncheck the box, try the download again and it should work for you.
This is simple to fix so if you run into this issue I hope this helps.