Getting 'Package not available' message

I've installed the dashboard. Searched for the required plugin... hit install and it said that we didn't have 'One Click Install' set up... I then followed the instructions to add the FTP details to the wp-config.php file. Now when I press install it says 'Error'. There's a button that say 'Package not available' and pressing it does not reveal any extra info. Not sure how to progress now?? Any ideas why this is happening?
Thanks in advance,

Dan