Mining stop working - ethminer

Everything was working fine this morning, now all of my miners stopped working - 4 different computers. Getting the same message:
miner 20:58:00|main Getting work package...
JSON-RPC problem. Probably couldn't connect. Retrying in 1...
miner 20:58:02|main Getting work package...
JSON-RPC problem. Probably couldn't connect. Retrying in 1...

Any idea??!?