I tried and tried again using format feature of Windows OS as mentioned above and failed every time! Finally I did it in another way!
I've solved this problem using a simple program written for Windows OS.
download the following program and use FAT32 for USB stick and "Quick Format". Now iLiad can see all documnets on USB Stick.
USB-Drive_Formater.zip
I think that this program helps my friends in this valuable forum.
Regards