Hi, thank you very much for your reply.

I am now using the 0.16 version and I used the following:

./minerd --user rpcuser --pass 111111 --url http://127.0.0.1:8961/ --threads 4 --coinbase-addr XQg3PmNxX9oEbxsymqtQHir6dkPpVPTJ6P --coinbase-sig "my test coins" -a sha256d -D

My bitcoin.conf is:

server=1
gen=0
rpcuser=rpcuser
rpcpassword=111111
rpcallowip=127.0.0.1
rpcport=8961
listen=1

However, I still get the same error:

[2018-04-29 03:21:00] Binding thread 0 to cpu 0
[2018-04-29 03:21:00] 4 miner threads started, using 'sha256d' algorithm.
[2018-04-29 03:21:00] Binding thread 3 to cpu 1
[2018-04-29 03:21:00] Binding thread 2 to cpu 0
[2018-04-29 03:21:00] Binding thread 1 to cpu 1
[2018-04-29 03:21:00] HTTP request failed: The requested URL returned error: 500 Internal Server Error
[2018-04-29 03:21:00] json_rpc_call failed, retry after 30 seconds
[2018-04-29 03:21:30] HTTP request failed: The requested URL returned error: 500 Internal Server Error
[2018-04-29 03:21:30] json_rpc_call failed, retry after 30 seconds
[2018-04-29 03:22:00] HTTP request failed: The requested URL returned error: 500 Internal Server Error
[2018-04-29 03:22:00] json_rpc_call failed, retry after 30 seconds
[2018-04-29 03:22:30] HTTP request failed: The requested URL returned error: 500 Internal Server Error