This happens for one of the following reasons:
The software settings in the configuration file do not match the physical hardware settings. Correct either one to match the other.
The ifconfig command pings to the wrong address. Verify the network mask and the sending and receiving IP addresses.
The target has an invalid IP address or does not have its TCP stack running. Check the destination computer to make sure it works properly.
A network card with two network connectors uses a different type of network connector than the software. Adjust the hardware or software to use the proper connector.
The network lacks one or more terminators. Install terminators at the ends of the network.