[Plugin: BackWPup] Cannot install plugin

I am unable to install the plugin:

Downloading install package from http://downloads.wordpress.org/plugin/backwpup.2.1.11.zip…

Unpacking the package…

Could not copy file. C:/Documents and Settings/Nick/My Documents/My Web Sites/wordpress/wp-content/upgrade/backwpup.tmp/

http://wordpress.org/extend/plugins/backwpup/