Error while reading from EM6436 energy meter.

We are using EM6436 energy meter connected to a PC via RS232 to RS485 converter.

With my own code using modbus4j open source library,we are able to discover the Energy meter and obtain its ID using Modbus4j.
But when I try to read data address (3901 say) of the device(EM6436) using the following code:<pre>
SerialParameters params = new SerialParameters();
params.setCommPortId("COM1");
params.setBaudRate(9600);
params.setDataBits(SerialPort.DATABITS_8);
params.setParity(SerialPort.PARITY_EVEN);
params.setStopBits(SerialPort.STOPBITS_1);
ModbusMaster master = null;
ModbusFactory factory = null;
try
{
factory = new ModbusFactory();
master=factory.createRtuMaster(params, 0);
if (master == null){
return;
}
master.setTimeout(5000);
master.init();
Object obj = null;
NumericLocator locator = null;
try{
locator = new NumericLocator(1,
RegisterRange.HOLDING_REGISTER, 3901, DataType.FOUR_BYTE_FLOAT);
obj = master.getValue(locator);

}catch (Exception e) {
System.out.println("Exception occured : "+e.getMessage());
}

System.out.println("Value read"+"for------"+i+"----------->"+obj);

}
}
finally {
master.destroy();
}
} </pre>
We are getting error as Error Response Exception :Invalid data address or sometimes its giving TimeOut exception.
The same code is working fine with the simulators (Modbus PAL , Modbus PLC).

Even reading the same data address with ModScan32 (with the same connection) is also working but not with the above code. Please suggest.