iwconfig and interesting problem

[Mohsen Pahlevanzadeh <mohsen pahlevanzadeh org>]

Dear all
When i use by hand iwconfig , i get following error:
debian:/home/mohsen# iwconfig wlan0 essid mohsen key s:googooli
Error for wireless request "Set Encode" (8B2A) :
    SET failed on device wlan0 ; Invalid argument.
debian:/home/mohsen# 
But i have a question:
How networkmanager can connect to access poin? if possible tell me that
i can try and connect.because networkmanagers's parameter that it
involved can help me.....
Yours,
Mohsen