How to reproduce

1.) Install 6u10 or 6u12

2.) Try to do a manual or auto upate

3.) As soon as you click on update balloon remove the network cable

You will see the error dialogs; for more info please see the attachment.
It is one dialog at a time; and it depends at what time you disconnect the internet connection. If you disconnect immediately it will show "NetworkFailureError.jpg" else it will show download failure dialog "DownloadFailureError.jpg".
There is no way we can find what is the actual cause of download failure. We need to make sure that we use correct wording to show the error logs. It will good; if we can just log the error instead of shwoing the error dialog in auto update mode.