Uninstall the driver of your USB from device manager.
1. Connect your USB
2. Click Start, and then click Run.
3. Type devmgmt.msc, and then click OK.
4. Device Manager opens.
5. Expand Universal Serial Bus controllers.
6. Right-click the USB controller under Universal Serial Bus controllers which you have connected, and then click Uninstall.
7. Restart your PC.
Now try to copy files and check if its happening again.
Good Luck.
Peace.