This isn't really a VCD question, more of an ESX or guest VM question.
In the guest VM, try edit the NIC, adapter configuration, and instead of auto-detecting the speed and duplex, set it to whatever it's supposed to be (i.e. full duplex and the correct speed).
If that doesn't help, try deleting the NIC and add a new one with a different NIC emulation (i.e. instead of E1000 try vmxnet3)