Add rufus.exe and temporary Rufus directory ( %TEMP%\Rufus ) to antivirus exclusion list (tested with Avast, AVG, and Symantec Endpoint Protection).
. Because Rufus requires exclusive access to the USB drive to format it and write boot files, any other process holding a "handle" on that drive will trigger this failure. Critical Fixes for Windows 7 rufus access to device denied windows 7
Windows 7 may have a corrupted partition table or an "active" flag that Rufus cannot overwrite. The solution is to scrub the drive clean using DiskPart. Add rufus