This is a known issue affecting VMware ESXi 5.1 Build 1065491.
Currently, there is no resolution.
To work around the issue, use the VMXNET3 virtual adapter and reduce the usage of the E1000 series adapter.
For more information on adding or modifying a virtual machines virtual network interfaces, see
the section
Change the Virtual Network Adapter (NIC) Configuration in the vSphere Web Client in the
Configuring Virtual Machine Hardware in the vSphere Web Client Guide.
Note:
If you encounter this issue: