(Help) Serial Communication Error on Uhf RFID device

hi, everyone thanks for taking time to read this. please help me with my connection to UHF RFID RM9001, i am using an rs810-105 To usb converter.
I have installed all the drivers needed for connecting with the RFID RM9001,
I also have tried in many types of operating systems like, win7x86, win7x64 and win8.1x64.
but all of this have the same error on the applications demo program.
it says "Serial Communication Error"...
i also have selected the right COMPORT for the device. but it also says "Serial Communication Error"
please help me what do i have to do with this error.:wave::wave::wave:
Attachment 35923