If your guest OS is windows servers, see whether you have hidden network adapters in device manager, uninstall them if they exist. Follow these steps
1. Open command prompt
2. Type set devmgr_show_nonpresent_devices=1 and then press ENTER.
3. Type Start DEVMGMT.MSC, and then press ENTER.
4. Click View, and then click Show Hidden Devices.
5. Expand the Network Adapters tree.
6. Right-click the dimmed network adapter, and then click Uninstall.
Thanks