1. You do not have a proper smbios.plist.
2. Ethernet is en1 rather than en0 (for machines without Ethernet, WiFi should be en0).
3. Ethernet is not being detected as built-in.
4. You are using a self-compiled kernel (such as the new AMD kernel), which is a kernel bug that needs to be fixed. No solution except to switch to the vanilla kernel (mach_kernel).
As any of these (or all of these) could be causing the issue, I suggest you troubleshoot in this order; reboot after each solution to see if it worked:
1. Download a proper smbios.plist. If you already have an smbios.plist, I recommend that you also download a new smbios.plist. It can be the same model as before, but you will use a known-good version. The easiest way to do this is to use the app Chameleon Wizard; simply download it and open it:
ChamWizard.png 97.89KB 180 downloads
Now click the SMBIOS tab:
SMBTab.png 106.13KB 172 downloads
Click Edit, and choose a predefined smbios.plist from Premade Smbioses; those who already have an smbios.plist can pick the same model they are currently using, and those who do not have an smbios.plist can pick one based on their CPU socket/type (Intel users) or whatever they like (AMD):
GSMB.png 148.57KB 151 downloads SMBIOS list.png 46.29KB 150 downloads
And save it. When you reboot you will have all the proper SMBIOS information you need.
2. en0 information is kept in the file NetworkInterfaces.plist, which can be found in /Library/Preferences/SystemConfiguration. Copy that file onto your desktop and open it. Locate:
<key>UserDefinedName</key> <string>Ethernet</string>A few lines above that, you should find:
<key>BSD name</key> <string>en0</string>If it is en0, Ethernet is set correctly. If it is en1 (or anything other than en0), change it to en0. If you had to change Ethernet to en0, look for en0 further down in the file above another network interface (WiFi, FireWire, etc.) and change it to en1 (or whatever Ethernet was before you changed it). If you don't have Ethernet on your computer, you will want your WiFi to be en0; in that case instead of looking for Ethernet under UserDefined name, you will look for Wi-Fi (Lion) or AirPort (Snow Leopard and earlier) and make the necessary changes.
Now save the file, and drag the new file from your desktop into /Library/Preferences/SystemConfiguration to replace the old file.
3. Activating built-in Ethernet is very simple. Go to /Extra and verify whether you have com.apple.boot.plist or org.chameleon.boot.plist; if you have org.chameleon, you can use Chameleon Wizard; simply click on the org.chameleon.Boot tab and select Ethernet Built In:
o.cham.png 138.03KB 157 downloads
Then click Save.
If you have com.apple, download Lizard and open it. It will open right where you need it to be; simply check the box for Built In Ethernet:
Lizard.png 75.51KB 136 downloads
Then click Save.