Symptoms:
VMware vSphere ESXi 7.0
VMware vSphere ESXi 8.0
This issue occurs because the flexible network adapter may not handle traffic reliably in newer 64-bit hypervisors.
Flexible network adapters not supported
For more information, see Choosing a network adapter for your virtual machine (1001805).
For more information on Windows 2003 compatibility, see the VMware Compatibility Guide.