Hi Peter,
This feature will no longer be maintained anymore, and it has been removed from 2.7. You still have the button because you have ever installed 2.6, if you didn't uninstall 2.6 but installed 2.7 directly, then those files will not be removed by 2.7, even you uninstall 2.7, and you'll see the button because uploading to minus is implemented as a plugin to DuckCapture, DuckCapture 2.7 find it and automatically loaded this plugin. But I cannot guarantee that it works in future. If you installed 2.7 on a clean machine, the button will not be there.
So my suggestion is, just leave it as is. If you do need this feature, you can install Minus Desktop Tool.
HTH,
Mason