[Ubuntu 14.4, nVidia 750 Ti 2GB] json_rpc_call failed
Hello, 
i did everything according to manual but when i try to start digging a get an error:

```
./xmrMiner --url=pool.minexmr.com:7777 --user=44[...]pZ --pass=x --retry-pause=5 -D
    *** xmrMiner 0.2.1 (64 bit) for NVIDIA GPUs by psychocrypt 
    *** Built with GCC 5.4  using the Nvidia CUDA Toolkit 8.0
[...]
-----------------------------------------------------------------
[2017-08-17 22:53:46] Using JSON-RPC 2.0
[2017-08-17 22:53:48] 1 miner threads started, using 'cryptonight' algorithm.
[2017-08-17 22:53:48] GPU #0: GeForce GTX 750 Ti (5 SMX), using 20 blocks of 8 threads
[2017-08-17 22:53:48] Tried to call rpc2 command before authentication
[2017-08-17 22:53:48] json_rpc_call failed, retry after 5 seconds
[2017-08-17 22:53:53] Tried to call rpc2 command before authentication
[2017-08-17 22:53:53] json_rpc_call failed, retry after 5 seconds
[2017-08-17 22:53:58] Tried to call rpc2 command before authentication
[2017-08-17 22:53:58] json_rpc_call failed, retry after 5 seconds
```

What can i do about it?