I have two Macbooks at home (Aluminum 2.4 GHz late fall 2008 and 1st-generation Macbook Air). I downloaded several updates, among which were Airport Client Update 2009-001 and Airport Utility Software Update 5.4.1 on my Aluminum Macbook. After the laptop restarted, I got a message saying that my system clock was incorrect and was set to before 2001. It is currently set to December 31, 2000. The time was incorrect as well. The Macbook is configured to use NTP, but the Wi-Fi connection wasn't working. I started investigating the issue and realized that the Airport Client Update 2009-001 broke Wi-Fi on my Macbook. My Macbook Air is still connecting fine. The Access Point is a Cisco 1140 access point that supports concurrent 802.11g and 802.11a. My home network is on 802.11a. I also have a wireless print server on 802.11a, which is also connected fine. I looked at the Console logs, and saw the following: "WLC_E_COUNTRY_CODE_CHANGED" en1: 80211d country code set to 'X0' On the Apple support forums site there are a few threads describing a similar issue after this update was downloaded, except most people use Time Capsule or Airport Extreme as the access point. It seems that if you are using the 5 GHz range (802.11a or 802.11n), and the SSID is hidden, the Airport Client Update 2009-001 breaks the connectivity. My Cisco access point is reporting the following in the log: Mar 11 22:14:42.227: %DOT11-7-AUTH_FAILED: Station 0023.1257.XXXX Authentication failedConnection closed by foreign host. I even re-did the Wi-Fi network configuration on the Aluminum Macbook to make sure that my previous settings were not corrupted. When I try to associate to the Cisco access point, the Macbook seems to connect for just a couple seconds and then it disconnects. Word of caution, do not install this update. It definitely has a bug.