Talking with my coworkers, this PLC don't have an access control list.
Code working if a use two PCs and modbus examples on LabVIEW as a modbus server. When Ido this I can read with my code.
Cheking with Wireshark, with PLC, the communication was disconnected before transfer any modbus packet. When running with two PCs I could see modbus packets on wireshark.
My challage is how identify what cause this disconnection.