Windows Explorer is often the culprit. If you have a window open showing the contents of the USB drive, TransMac will be blocked. Close all File Explorer windows.
Search for in your Start menu, right-click it, and Run as Administrator . Type diskpart and press Enter.
Check your System Tray (bottom right corner). Close any disk utilities, antivirus scanners, or cloud storage apps (like OneDrive or Dropbox) that might be "watching" the drive for changes. 3. Use Diskpart to Clean the Drive (Most Effective)
Sometimes, real-time protection sees TransMac's attempt to write a macOS file system as "suspicious activity" and locks the drive to prevent what it perceives as a boot sector attack.