aircrack not working even with wpa key in dictionary

[Luca Ferrari]

Hi all,
to test my wireless network I played with airodump and aircrack following the 
tutorial here:http://www.ubuntu-unleashed.com/2007/08/howto-aircrack-ng-quick-
and-simple.html.

Now I've captured packets untill airodump presented me the WPA-PSK handshake 
title in the top right corner of the screen. Then I stopped the program 
airodump, and tried to guess the passprhase using the dictionary of john the 
ripper:

aircrack-ng -w /usr/share/john/password.lst *.cap

and the program quitted after testing (only) 472 keys without founding the 
right one. So I added the right passphrase to the dictionary, as last entry, 
and ran it again, but the system is still unable to guess the passphrase.  Am 
I doing something wrong?

Luca