Communicate Between Two XBee Devices

Before going further,the first step to understand in XBee operation is trying to communicate it between each other (TX-RX) in bidirectional mode..I need to install the driver at 2 PC's which is USB Serial Converter and USB Serial Port..This is to make the XBee compatible with the PC's..After that the X-CTU software need to be installed.

This software will enable user to send and receive a data at a time.The are several configuration need to be determine first such as the Baud Rate = 9600, data bits=8 and stop bits = 1..After that, we must enter the command mode by typing +++ into the terminal area and after that the Xbee's are ready to be operated..The simple diagram on how the XBee communicate is shown below.

But there is a bit problem on communicate the XBee's..The another XBee modules can't be detected by PC..It said "Unable to communicate with the moderm"..This happened at one side only..In my opinion there is something wrong either the hardware or the driver..