aireplay-ng deauth not doing anything

I just installed aircrack-ng via macports. Also installed the required libraries (openssl,sqlite3).

However when I try the simple deauth command the output is nothing.

example:

aireplay-ng -0 1 -a xx:xx:xx:xx:xx:xx -c XX:XX:XX:XX:XX:XX en4

when I press enter nothing outputs.

Has any1 any ideas what is going on here?