[Plugin: Scroll to Top Plugin] automatic add new plugin – broken

Because the plugin .zip file is within another .zip file
the automatic add new plugin method does not work

Download and unzip the outer folder (from the wordpress.org site). Upload the inner zip folder to your plugin folder (using FTP)
Upload inner zip file using the add new plugin option – in your wordpress blog admin area.

http://wordpress.org/extend/plugins/scroll-to-top-plugin/