I had a similar problem. Could see games, and had set up WET11 MAC in Advanced Settings, but when I connected to a game it would immediately drop and tell me the connection was lost. This fixed it.
Go to your wet11 setup (i.e. in the browser) and turn on "Enable MAC Address cloning" (top right in my Firmware Version: 1.5.4). Hit "Apply". When the page reloads, the WET11's MAC Address will be 00:00:00:00:00:00. This is what you want.
Now start X-Link and make the X-Box look for games. You'll see the Local X-Box show up with its real MAC Address (should be 0050...). If you don't have "Enable MAC Address cloning" turned on, you'll see the MAC address of your WET11 - no good (should be, but it isn't).
It seems that X-Link disregards non-X-Box Mac Addresses when you actually connect to games. The WET11 nomination stuff in the Advanced Setting seems to have no impact on whether or not X-Link sees the X-Box. I was able to see games and connect, but it would immediately drop when I joined the game. Now all fixed.
tedtedson <