Capturing handshake packets

Hi to all! I'm using Wireshark in BackTrack, with an Alfa AWUS036H as wireless interface, put in monitor mode. I'm trying to analyze the traffic in my wireless network: if there's no protection, I can capture the packets and analyze them; if the network is protected with WPA, following this guide: http://wiki.wireshark.org/HowToDecrypt802.11

I added the wpa-psk in the preferences. So, I can capture the packets, but I can't decrypt them. Then, I discovered that I need 4 handshake packets, so I disconnected and reconnected a client to the AP to get them, but still can't decrypt the packets. Analyzing the traffic using as filter "eapol", I can see several packets, named: Key (msg 1/4) Key (msg 2/4) Key (Group msg 1/2) Key (Group msg 2/2)

My question is: since I need 4 handshake packets and I can see only Key (msg 1/4) and Key (msg 2/4) (I don't know about Group msg... - maybe broadcast packet?), this means I'm missing Key (msg 3/4) and Key (msg 4/4)? Or I have another problem that doesn't allow me to decrypt packets?

Many thanks in advance for your help! :)