I guess you are using LabVIEW. Have you tested the example USB Raw –Bulk.vi from LV NI Example Library? This example should work properly for you.LAbVIEW>>Help>>Find Examples>>search for USB >>choose USB Raq-Bulk.vi
Before you run this VI, install a USB RAW device and configure NI Measurement & Automation Explorer (MAX) to recognize the USB device. You can read to and write from the USB RAW device only after you install and configure the USB RAW device and open a session to the device.
In my opinion, the attached KnowledgeBase could be helpful. This document includes a lot of details about your issue.
How Can I Communicate With a Device Using NI-VISA USB RAW Mode?