Poloniex has disabled litecoin deposits and withdrawals. Make sure not to send anything to poloniex's LTC address.
LTC is currently under maintenance or experiencing wallet/network issues. Deposits and withdrawals will remain disabled until a solution is found, which may require an update from the LTC team. Any updates must be tested and audited before enabling.
When will it come back on?
Already back up
That was fast. Meanwhile ZEC, BCN currencies are still disabled.