Why am I getting this error
[2014-05-20 07:53:49] accepted: 1/1 (100.00%), 31.93 H/s at diff 2000 (yay!!!)
[2014-05-20 07:53:49] thread 0: 66 hashes, 32.22 H/s
[2014-05-20 07:53:50] thread 1: 49 hashes, 32.03 H/s
[2014-05-20 07:53:51] json_rpc2.0 error: Duplicate share
[2014-05-20 07:53:51] submit_upstream_work json_rpc_call failed
[2014-05-20 07:53:51] ...retry after 10 seconds