Did you ever had a problem to unmount a drive/share on a linux system? Maybe the mount share is not accessible but the mount still there.
umount /mnt/blah
unmount error 16 = Device or resource busy
Refer to the umount.cifs(8) manual page (man 8 umount.cifs)
You can do the following:
umount -f /mnt/blah
If it doesnt work, use the lazyness method:
umount -l /mnt/blah
Test if your mount is still mounted with the command mount
What man say about umount
man umount
-f Force unmount (in case of an unreachable NFS system). (Requires
kernel 2.1.116 or later.)
-l Lazy unmount. Detach the filesystem from the filesystem hierar-
chy now, and cleanup all references to the filesystem as soon as
it is not busy anymore. (Requires kernel 2.4.11 or later.)


If you want to know what processes are keeping the filesystem busy, you can do:
fuser -m /mnt/blah