OS X doesn’t mount NTFS disks if Parallels VM is running.
Our investigation shows that “prl_disp_service” (a part of Parallels Desktop solution) automatically unmounts NTFS volume every time it appears. So NTFS partition mounts fine
but then prl_disp_service unmounts it for some reason.
Embedded Read-only NTFS driver shows the same behaviour. So it seems that our solution is not related to this issue at all.
Until now, the only possible solution is to disable the Parallels application.
Alternatively you can Unmount, and then Mount the disk using preference pane interface, but you will have to do this each time.