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,