I have 2 defect interface for USB-RS232 converter.
First interface :
please just try to establish a communication using a standard null modem cable connecting the USB2RS232 with a generic COM port.
When doing so, I recognized that the communication only worked in one direction, which means that I was able to send something thru your interface but interface was not able to transfer incoming data to the PC. I ran communication without software/hardware handshake.
You can easily reproduce the problem by opening two sessions of a terminal program on the PC and trying to communicate between them.
Second interface :
When plugging in the second interface that I got, Windows comes up with an error message in the hardware wizard:
"An error occured during the installation of the device: The installation failed because a function driver was not specified for this driver instance."
This problem was also reproducable and appeared independently whether the first interface was plugged in too or not.