mac unable to log onto active directory - mac shakes its head at you at log on prompt

run the below in terminal

sudo dsconfigad -localhome disable
sudo dsconfigad -useuncpath disable

man page here https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man8/dsconfigad.8.html

file permissions not inherited on a a network drive with a mac client

If files are cut/pasted from another folder they retain the original permissions, as opposed to copying and pasting which will inherit the permissions from the ( new) parent folder.

getting access to a mac when you don't have the password or have forgotten it

I recently came across a mac where none of the known passwords worked, including the root account. 

If you boot from an external drive you can copy a known good plist file into the following folder

/var/db/dslocal/nodes/default/users/user.plist

You can copy the plist file from your own machine ( that way you know the password). Then just rename to match the user account you want access to.