Ever since I installed Mac OS X 10.5.7 on my Intel Core Duo iMac, I've had ethernet disconnection problems. Prior to 10.5.6 I had no problems with ethernet. I keep the iMac connected to Internet Relay Chat all day, so every time the ethernet disconnects, my machine leaves the chat room. In the chat transcripts, I can see exactly when the disconnections occur and how often. It happens many times a day since I installed 10.5.7. Whenever there's a disconnect from IRC, I can see messages in the system log at the exact time the disconnect occurs: kernel[0]: AppleYukon2: 00000001,00000000 sk98nif - deadmanCheck - nothing received, resetting chip kernel[0]: AppleYukon2: error - Event scheduler called in Init Level 0 or 1 kernel[0]: AppleYukon2: error - FATAL: SkGeStopPort() does not terminate (Rx) kernel[0]: AppleYukon2: error - Event queued in Init Level 0 kernel[0]: Ethernet [AppleYukon2]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug I see many such message in the log. I've attached the file "yukon.txt" showing a number of the messages from "system.log". According to Software Update, I installed 10.5.7 on 5/13/2009. When I search my system.log archives (system.log.0.bz2 through system.log.7.bz2) for "deadmanCheck", I find a lot of them starting 5/13 and continuing through today; however, I find absolutely none of those messages prior to 5/13. For my internet, I have a cable modem. Attached to the cable modem is a dual-band AirPort Extreme base station. There are three machines connected to the base station: the aforementioned Intel Core Duo iMac via ethernet, an iMac G4 via ethernet, and an Intel Core 2 Duo MacBook Pro via wifi (5 GHz). The crucial thing is that only the Intel iMac has disconnection problems. All three computers are connected to the base station at the same time, but at the same time the Intel iMac disconnects, the other two machines do not. The iMac G4 is running Mac OS X 10.4.11, so it is not affected by the 10.5.7 regression. The MacBook Pro is running 10.5.7, but it is connected via wifi rather than ethernet. Note that I tried switching the ethernet cables for the Intel iMac and the iMac G4 as a test. When the iMac G4 uses the same ethernet cable and ethernet port on the base station that the Intel iMac was using before, the G4 does not disconnect. The Intel iMac does disconnect, however, using the cable and port that the G4 was using before. Thus, it's not a problem with the ethernet cable or the base station but rather a problem with the Intel iMac. Finally, I note that a number of other people have mentioned that they have had the same ethernet problems starting with Mac OS X 10.5.7. You can find references to this on the Apple Support discussion boards. For example: http://discussions.apple.com/thread.jspa?messageID=9467079 http://discussions.apple.com/thread.jspa?messageID=9477314 Please fix this regression ASAP. It's rendering ethernet on my iMac almost unusable because of the frequent disconnects.