The MVI71-DNP User Guide states that you should configure your terminal emulation software to 57,600 baud, 8 data bits, no parity, 1 stop bit, no hardware handshaking. In MVI71-DNP configuration, there is a parameter that sets the baud rate for the configuration port.
In some sample ladders that went out, this parameter is set to a value of 0, which sets the configuration port baud rate to 300 baud. This parameter is located at N7:58 in the sample ladder logic. Place a value of 57,600 here to set the configuration port baud rate to the proper value.