automounter problem

[Dan Alexander]

We use NIS to automount home directories, and every once in a while, the mounts get hung. problem is, I CANNOT umount manually the /home/user dir, and remount. When I do try umount, umount comes back with a " Block device required" error. It seems the only way to fix this is to reboot, which is not an option in the middle of the day! Is there a way to manually FORCE this to be unmounted? Any help would greatly appreciated...