NFC errors result from networking issues. Your best approach is to simplify the networking environment for the purpose of your conversion. Referencing VMware KB Article 1004615, here are several things to check and try:
- Verify that non of the NICs involved in the conversion have been statically configured to be at a different speed or duplex.
- Ensure that the NICs and switches in the conversion environment have matching speed and duplex settings.
- Connect the source and destination servers to different ports on the switch
- Swap the network cables with known good ones
- Use a crossover cable between the source and destination servers
If that is not an option, or if it does not fix this issue, the ultimate workaround is to convert the source machine to a hosted virtual machine destination, such as VMware Workstation. You could then use scp, winscp, etc., to copy the converted virtual machine files to your ESXi server. You must use
vmkfstools -i to import the virtual machine. (source)