Mounty is a tiny tool to re-mount write-protected NTFS volumes under Mac OS X in read-write mode.
However, sometimes you will see this error when you run it.
Error: Volume not re-mountable. The volume is not re-mountable in read/write mode. Probably it was not clean unmounted before.
If this error occurs, you can use the following workaround.
After reconnecting the external disk in the Windows OS, select “Safely Remove” from the system tray to extract the external disk and connect it to Mac OS again.