I believe this happens because one or more of the low level processes that manage networking for Fusion (the vmnet-* processes) gets stuck or Fusion is otherwise unable to communicate with them. When that happens, Fusion can be restarted, network adapters removed and added again, but it still won't help because from Fusion's perspective, it has no control over low level network settings through those processes, so the settings are shown as being unavailable for editing.
When you restart Fusion, it does try to start those processes again under its own control, but it notices they're already running and stops trying, and Fusion ends up in this state where network services are in fact running, but the settings to control them are unavailable.
As a symptom of this issue, you can check system.log in Console and you may notice messages like:
VMware Fusion 2235595[70158]: Error: Unable to start the bridge services. Error: /Applications/VMware Fusion.app/Contents/Library/vmnet-bridge is already running, process ID: 2852 [1]
To fix it, either reboot, or alternatively this should work:
- Shut down all running VMs
- Quit VMWare Fusion
- Open Activity Monitor
- Quit or force quit any vmnet-* processes that are still running
- Restart VMWare Fusion, it should automatically start any of those processes you killed earlier
As I said you'll probably get the same effect by just rebooting, but sometimes that's not an option for various reasons.
Once you do that, network settings should work again.
