Slingbox Software upgrade gives "Invalid Firmware" error

In some cases, when trying to upgrade Slingbox Software, you get the error, Invalid Firmware. You may also notice that the browse-to path shows C:\fakepath\SlingboxCurrent.bin.

If that happens, here's what you can do:

Exit the Setup Assistant, as well as SlingPlayer for Windows.
Open a new web browser page using Microsoft Internet Explorer
Choose Internet Options from the Tools menu, then click the Security tab.
Click Custom level.
Enable the option Include local directory path when uploading files to a server.
Click OK, then click OK again to dismiss the dialog boxes.
Relaunch SlingPlayer for Windows and try the firmware upgrade again.