mijngebruikersnaam on "[Plugin: Jetpack by WordPress.com] 'install now' button at plugin section disappeared"

The "install now" button (next to the Details button) at the plugin section diasappeared (at the 'jetpack from wordpress.com' plugin)
I really need it :/
I can't find how to solve this on the internet or this forum :(

Thanks in advance !

http://wordpress.org/plugins/jetpack/