I get these every time I run cpuminer
[2013-12-28 01:09:51] thread 3: 4 hashes, 1.97 khash/s
[2013-12-28 01:10:07] JSON-RPC call failed: {
"message": "upstream RPC error",
"code": -4
}
[2013-12-28 01:10:07] submit_upstream_work json_rpc_call failed
[2013-12-28 01:10:07] ...retry after 30 seconds