I got an ALFA AWUS036H for some wireless testing. I had trouble getting deauthentication to work. Eventually I ran across this post

http://forum.backbox.org/software-support/aireplay-ng-ignore-negative-one/

I’ve encountered this error in the past many times. I own four different Alfa wireless NICs, and to get around this problem all I have to do is:
service network-manager stop
airmon-ng check kill && airmon-ng start wlan0
ifconfig wlan0 down
airodump-ng -f 1000 mon0 (as an example)

I usually double check wpa_supplicant is not running as it does seem to affect monitor mode.

killall wpa_supplicant

You’re monitor interface (eg mon0) will still be available even after putting your primary wireless interface (eg wlan0) down. This fixes the -1 channel issue for me without patching any drivers.

This made it work for me

Also, to bump the trsx http://fl3x.us/blog/2013/01/12/setting-alfa-awus036h-to-30-dbm-1w-in-backtrack-5-r3/

Also, this command is useful after a capture

wpaclean <What you want the output cap file to be called> <cap file to clean>