When we got our first couple docking stations, it turns out that one worked and one was bad--it kept dropping the connection and switching between wired and WiFi. I thought it was a WiFi issue, but after finding that the machine was working with the other dock, it quickly became obvious that the dock itself was the issue. After getting a replacement, the problems went away.
A couple things to check:
- Do you have WiFi enabled as well? You might try turning that off just for troubleshooting purposes.
- Do you have a USB Ethernet dongle? That might help narrow the issue as well.
If not the dock, maybe it's a networking issue, like running out of addresses in the DHCP pool?