Cisco wireless connectivity issues

Strange situation. I have a Macbook Pro running SL 10.6.8 (all updates). Until last week I had no problems connecting to the wireless network at work. The wireless is based on Cisco and configured with 802.11 b/g. Wireless security is setup to use WPA-PSK. (or WPA2-PSK, not quite sure).

What happens is that my Macbook does not get an IP address (only the 169.x.x.x). The log at the Cisco AP shows "association error". If I remove the wireless network from my key chain, and tries to connect again (entering the PSK password once again), I get the same error. The strange thing is that when I connect, and if I enter the wrong password, my Macbook will not connect. But if I enter the correct password, and my macbook connects, I still do not get an IP address and the Cisco AP still says "association error".

This worked 100% until last week. There have been (100% sure) done no changes to the Cisco AP setup. But I do think that a major security update was done to the Macbook (SL 10.6.8) last week, but I am not sure.

Anyway, have anybody got any ideas ? How do I start debug ? I am the only one with problems. We have both PC's and Mac's at work. The PC's are running Windows 7 and the 2 other Mac's are running Lion. I can not upgrade yet due to software issues.

I connect to a D-Link wireless network at home, configured with WPA2-PSK (AES encryption) without any problems (using 5 Ghz 802.11n or 2.4 Ghz 802.11g).