The term communication error or transmission error simply refers to an error between the communications of one system and another. Many communication errors are harmless, as they are often stopped by the software's error trap. For example, in Pokémon Diamond and Pearl most communication errors in the Global Trading System displayed the message "Communication error!" and logged the player out of the system.
Some communication errors are not stopped by an error trap however, for example, if the link cable is loose in a battle against another player glitchy effects can occur. This is especially true in Generation I and Generation II of the handheld Pokémon games, as the older Pokémon games tend to have upgraded engines which will 'trap' many more communication errors.
A communication error can be guaranteed by the partial trapping move Link Battle glitch immediately after the Pokémon sent out that takes the partial trapping move faints.