Malformed login packet
"Malformed login packet" is a client error that typically results from a problem with an internet connection, such as briefly losing a wireless signal. The problem could be in a wireless card, a router, or an internet service provider. Sometimes the loss of connection is only brief enough to notice drops in online games, but not streamed video or chat programs.
If in case you're in a combat situation and it happens, always keep your ring of death equipped (assuming that is above 15% charges) to prevent loss of items, familiar, etc. the next time you log back in.