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Modbus RTU on RS485 Master not processing

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I am using the Modbus RTU library for Arduino for TIVA TM4c1294ncpdt.


Slave(Modbus_Slave Software on PC) is responding to master request  but master somekind does not proccess informations that he gets. So I can not regulate LED on master side over potentiometer on slave side. Also master stops sending request to slave after 10 requests sended to slave (when retry_count is set to 5). 

Problem is: 
1) master send request to slave, 
2) slave gets request 
3) slave process request, 
4) slave returns answer to master
5) master gets answer 
6) master do not process slave answer

After 5 requests (10 actually: PRESET_MULTIPLE_REGISTERS - 5 times and  READ_HOLDING_REGISTERS - 5 times), master stops sending request to slave, due to retry_count which is set to 5. If I set retry count to 5000000, it still stops sending requests.

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