Stand-alone machines with no Ethernet port connection get this error when the system tries to access the network. If the Ethernet cable is connected, this message could result from a mismatch between the machine's NVRAM settings and the Ethernet hub settings.
If this message is continuous, try to save any work to a local disk.
When a machine is configured as a networked system, it must be plugged into the Ethernet with a twisted pair J45 connector.
If the Ethernet cable is plugged in, find out whether or not the Ethernet hub does a link integrity test. Then become superuser to check and possibly set the machine's NVRAM. If the hub's link integrity test is disabled, set this variable to false.
# eeprom | grep tpe tpe-link-test?=true # eeprom 'tpe-link-test?=false'